Finding a satisfying dinner that pleases the whole family while using pantry staples can feel like an impossible task. Between busy schedules, picky eaters, and the pressure to get something nutritious on the table without breaking the bank, weeknight meal planning often becomes more stressful than it needs to be.
That’s where this tuna casserole au gratin comes to the rescue: it’s comforting and filling, uses simple ingredients you probably already have, and delivers that crispy, cheesy top that makes everyone forget they’re eating something so budget-friendly.
Why You’ll Love This Tuna Casserole Au Gratin
- Low-carb comfort food – Using cauliflower instead of pasta makes this a keto-friendly version of the classic casserole that still feels indulgent and satisfying.
- Quick weeknight dinner – Ready in just 25-35 minutes, this casserole is perfect when you need something hearty on the table fast.
- Pantry-friendly ingredients – Built around canned tuna and simple ingredients you likely already have, making it great for those nights when you haven’t planned ahead.
- Rich, cheesy goodness – The combination of mozzarella and gruyere creates a bubbly, golden top that makes this casserole feel special enough for company.
- High-protein meal – Packed with tuna and cheese, this dish will keep you full and satisfied without weighing you down.
What Kind of Tuna Should I Use?
For this casserole, you’ll want to stick with canned tuna in springwater rather than oil-packed varieties since we’re already adding plenty of richness with the mayonnaise and cheese. Solid white albacore tuna gives you nice, meaty chunks that hold up well in baking, but chunk light tuna works great too and is usually more budget-friendly. Make sure to drain your tuna really well before mixing it in – nobody wants a watery casserole! If you’re feeling fancy, you can even use jarred tuna, which tends to have larger, more tender pieces, though it’ll cost you a bit more.
Options for Substitutions
This creamy casserole is pretty forgiving when it comes to swaps, so here are some easy substitutions:
- Canned tuna: You can use tuna packed in oil instead of springwater – just drain it well. For a different protein, try canned salmon, cooked chicken, or even leftover turkey.
- Mayonnaise and sour cream: If you want to lighten things up, replace half the mayo with Greek yogurt. You can also use all sour cream or all mayo if that’s what you have on hand.
- Gruyere cheese: This cheese can be pricey, so feel free to use Swiss cheese, sharp cheddar, or even more mozzarella. The flavor will be a bit different but still delicious.
- Cauliflower: Not a cauliflower fan? Try cooked broccoli, diced zucchini, or even cooked pasta like penne or shells for a more traditional casserole feel.
- Green onions: Regular yellow onion works fine – just use about 1/4 cup diced. You could also try chives or even diced celery for some crunch.
- Dijon mustard: Yellow mustard or whole grain mustard will work in a pinch, though the flavor will be a bit milder.
Watch Out for These Mistakes While Baking
The biggest mistake when making tuna casserole is not draining the canned tuna well enough, which can make your entire dish watery and prevent the cheese from melting properly – press the tuna with paper towels or let it sit in a fine mesh strainer for a few minutes to remove excess moisture.
Another common error is overcooking the cauliflower beforehand, since it will continue cooking in the oven and can turn mushy – aim for just tender when you pre-cook it, and let it cool completely before mixing with the other ingredients.
Don’t skip grating your own cheese if possible, as pre-shredded cheese contains anti-caking agents that can prevent smooth melting, and make sure to save some cheese for the top to get that golden, bubbly finish.
Finally, let the casserole rest for about 10 minutes after baking so the creamy mixture can set up properly and won’t run all over your plate when you serve it.
What to Serve With Tuna Casserole?
This rich and cheesy tuna casserole pairs perfectly with a crisp green salad dressed with lemon vinaigrette to cut through all that creamy goodness. I love serving it alongside some steamed green beans or roasted broccoli to add some fresh vegetables to the plate. A slice of crusty French bread or dinner rolls work great for soaking up any extra cheese sauce, and they help make the meal feel more complete. For a lighter option, try serving it with a simple cucumber and tomato salad or some pickled vegetables to balance out the richness of the casserole.
Storage Instructions
Refrigerate: This tuna casserole keeps really well in the fridge for up to 4 days when covered tightly with foil or plastic wrap. I actually think it tastes even better the next day after all those flavors have had time to meld together. Just make sure to let it cool completely before covering to avoid condensation.
Freeze: You can definitely freeze this casserole for up to 3 months, which makes it perfect for meal prep. I like to portion it into individual servings in freezer-safe containers so I can grab just what I need. The cheese might change texture slightly after freezing, but it still tastes great.
Warm Up: To enjoy your leftover casserole, just pop it in a 350°F oven for about 15-20 minutes until it’s heated through and bubbly again. If you’re reheating from frozen, thaw it overnight in the fridge first, then add an extra 10 minutes to the heating time. You can also microwave individual portions on medium power, stirring halfway through.
| Preparation Time | 10-15 minutes |
| Cooking Time | 15-20 minutes |
| Total Time | 25-35 minutes |
| Level of Difficulty | Easy |
Estimated Nutrition
Estimated nutrition for the whole recipe (without optional ingredients):
- Calories: 1700-1900
- Protein: 160-180 g
- Fat: 120-135 g
- Carbohydrates: 25-35 g
Ingredients
For the casserole mix:
- 20 oz canned tuna in springwater, drained
- 1 cup mayonnaise
- 1/3 cup sour cream
- 2 tbsp dijon mustard
- 1/2 tsp salt
- 1/2 tsp black pepper
- 1/4 tsp smoked paprika
- 1/2 cup chopped green onions
- 2 cups cooked and chopped cauliflower
- 1 cup shredded mozzarella cheese
For the topping:
- 1 cup shredded gruyere cheese
Step 1: Prepare the Oven and Baking Dish
Preheat your oven to 180°C (350°F).
While the oven is heating, grease a large baking dish with a little oil or nonstick spray to ensure your casserole doesn’t stick after baking.
I always like to grease the dish generously, which makes serving and cleaning up much easier.
Step 2: Mix the Tuna Filling
- 20 oz canned tuna in springwater, drained
- 1 cup mayonnaise
- 1/3 cup sour cream
- 2 tbsp Dijon mustard
- 1/2 tsp salt
- 1/2 tsp black pepper
- 1/4 tsp smoked paprika
- 1/2 cup chopped green onions
- 2 cups cooked and chopped cauliflower
- 1 cup shredded mozzarella cheese
In a large mixing bowl, add the drained tuna and use a fork to flake it into smaller pieces.
Stir in the mayonnaise, sour cream, Dijon mustard, salt, black pepper, smoked paprika, and chopped green onions.
Mix everything together until you have a well-combined and smooth mixture.
Then, gently fold in the cooked and chopped cauliflower and shredded mozzarella cheese until everything is evenly distributed.
Step 3: Assemble the Casserole
- tuna mixture from Step 2
- 1 cup shredded gruyere cheese
Transfer the tuna mixture from the bowl into the prepared baking dish.
Spread it out evenly so it bakes uniformly.
Sprinkle the shredded gruyere cheese over the top, creating a nice layer that will melt and form a golden crust.
Step 4: Bake the Casserole
Place the assembled dish in the oven and bake for 15-20 minutes, or until the cheese topping is bubbling and golden brown.
Keep an eye on the casserole toward the end of baking time to prevent the cheese from over-browning.
I like to bake until the edges are slightly crispy for extra texture.
Step 5: Serve
Remove the casserole from the oven and let it sit for a minute to cool slightly, which makes it easier to serve.
Scoop into bowls or onto plates and enjoy while hot.
Mouthwatering Tuna Casserole Au Gratin
Ingredients
For the casserole mix:
- 20 oz canned tuna in springwater, drained
- 1 cup mayonnaise
- 1/3 cup sour cream
- 2 tbsp Dijon mustard
- 1/2 tsp salt
- 1/2 tsp black pepper
- 1/4 tsp smoked paprika
- 1/2 cup chopped green onions
- 2 cups cooked and chopped cauliflower
- 1 cup shredded mozzarella cheese
For the topping:
- 1 cup shredded gruyere cheese
Instructions
- Preheat your oven to 180°C (350°F). While the oven is heating, grease a large baking dish with a little oil or nonstick spray to ensure your casserole doesn't stick after baking. I always like to grease the dish generously, which makes serving and cleaning up much easier.
- In a large mixing bowl, add the drained tuna and use a fork to flake it into smaller pieces. Stir in the mayonnaise, sour cream, Dijon mustard, salt, black pepper, smoked paprika, and chopped green onions. Mix everything together until you have a well-combined and smooth mixture. Then, gently fold in the cooked and chopped cauliflower and shredded mozzarella cheese until everything is evenly distributed.
- Transfer the tuna mixture from the bowl into the prepared baking dish. Spread it out evenly so it bakes uniformly. Sprinkle the shredded gruyere cheese over the top, creating a nice layer that will melt and form a golden crust.
- Place the assembled dish in the oven and bake for 15-20 minutes, or until the cheese topping is bubbling and golden brown. Keep an eye on the casserole toward the end of baking time to prevent the cheese from over-browning. I like to bake until the edges are slightly crispy for extra texture.
- Remove the casserole from the oven and let it sit for a minute to cool slightly, which makes it easier to serve. Scoop into bowls or onto plates and enjoy while hot.
