Preheat your oven to 350°F (175°C). Begin by gathering and prepping all your ingredients. In a medium skillet, heat the olive oil over medium to low heat. Add the finely chopped red onion, garlic cloves, celery, red bell pepper, and chopped green beans. Sauté until the onions are translucent and the vegetables are slightly softened, about 5-7 minutes. Remove from heat and let the mixture cool slightly before the next step.

In a medium to large mixing bowl, combine the sautéed vegetable mixture from Step 1 with the drained tuna, mayonnaise, and shredded cheddar cheese. Mix thoroughly so everything is evenly incorporated. If you like, you can stir in some cooked noodles at this stage for a heartier casserole. I find it helpful to let the sautéed veggies cool for a few minutes before combining so they don't melt the cheese right away.

Transfer the tuna and vegetable mixture from Step 2 into a casserole or baking dish, spreading it evenly. Sprinkle the almond meal or almond flour over the top to create a light, crunchy topping.

Place the casserole dish in the preheated oven and bake for 20-25 minutes, or until the cheese is melted and the topping is lightly golden. This step gives the casserole a nice texture and flavor. I always check at the 20-minute mark to avoid over-baking.

Remove the casserole from the oven and allow it to cool slightly before serving. Taste and season with salt and black pepper as desired. For extra flavor, I sometimes add a dash of black pepper just before serving. Enjoy your casserole alongside a fresh salad or your favorite veggies.