Preheat your oven to 425°F. While it heats, prepare all your ingredients: mince the garlic cloves, slice the mushrooms into 1/4-inch pieces, cut the chicken into 1-inch chunks, and measure out the milk, broth, spices, and spinach. Having everything ready before you start cooking will make the next steps smooth and stress-free.

Melt the butter in a large oven-safe skillet or Dutch oven over medium heat. Once melted, whisk in the flour and cook for 3 minutes, stirring constantly—this cooks out the raw flour taste and creates the foundation for your sauce. Gradually pour in the milk and chicken broth while whisking to prevent lumps, then simmer for 5 minutes, stirring occasionally, until the sauce thickens enough to coat the back of a spoon.

Remove the sauce from heat and stir in the nutmeg, onion powder, minced garlic, thyme, lemon zest, salt, and pepper. I like to add the garlic after the sauce cools slightly so its flavor stays bright and fresh rather than becoming bitter from the heat. Now add the chicken chunks and sliced mushrooms directly to the sauce, stirring to combine everything evenly.

Add the gnocchi and fresh spinach to the skillet, stirring gently for about 30 seconds until everything is just combined. The spinach will begin to wilt from the heat of the sauce—you don't need to fully wilt it at this stage since it will cook more in the oven. Make sure the gnocchi is evenly distributed throughout the mixture so it cooks uniformly.

Top the entire mixture with the shredded parmesan cheese—I prefer freshly shredded for better texture and moisture. Transfer the skillet to the preheated 425°F oven and bake for 15-20 minutes until the sauce is bubbling around the edges and the chicken is cooked through. For a golden, slightly crispy top, finish under the broiler for 2-3 minutes, watching carefully to avoid burning. Let rest for a minute before serving.