Preheat your oven to 350°F (175°C).

In a large pot of boiling salted water, cook the lasagna noodles according to the package instructions until they reach al dente, usually about 8-10 minutes.

In a medium saucepan over medium heat, melt 4 tablespoons of butter. Once melted, whisk in 4 tablespoons of flour to create a roux and cook for about 1 minute until bubbly. Gradually whisk in 4 cups of whole milk, stirring constantly for about 5 minutes or until the sauce thickens to a creamy consistency. Add garlic powder, onion powder, salt, and pepper, blending well before removing from heat.

Stir in 2 cups of shredded mozzarella and ½ cup of grated Parmesan cheese into the thickened sauce, mixing until melted and smooth.

In a 9x13-inch baking dish, spread 1 cup of your cheese sauce evenly across the base. Lay down 3 noodles, then add half of the ricotta cheese mixture, followed by half of the shredded rotisserie chicken. Top this with 1 cup of the creamy sauce, ensuring even coverage. Repeat the layering process with another set of noodles, ricotta, chicken, and sauce.

For the top layer, arrange the remaining noodles and pour the rest of the cheese sauce over them. Sprinkle the rest of the mozzarella and Parmesan cheese on top.

Place the assembled lasagna in the preheated oven and bake uncovered for 30-35 minutes. Let it rest for at least 10 minutes before slicing.

After resting, cut the lasagna into squares and serve it warm.