Preheat your oven to 350°F (175°C). Cook the tortellini according to package instructions, drain, and set aside.
In a large saucepan over medium heat, melt the butter. Stir in the flour and cook for about 2 minutes, until lightly browned.
Gradually whisk in the milk and chicken broth until the mixture is smooth. Continue to cook, stirring constantly, until the sauce thickens, about 5-7 minutes.
Stir in 3/4 cup of the mozzarella cheese and 3/4 cup of the Parmesan cheese until melted and smooth.
Add the garlic powder, onion powder, dried basil, dried parsley, salt, and pepper. If using, stir in the chopped spinach until wilted.
In a large mixing bowl, combine the cooked chicken, tortellini, and the cheese sauce.
Mix until everything is well coated.
Transfer the mixture to a greased 9x13-inch baking dish. Sprinkle the remaining mozzarella and Parmesan cheese over the top.
Sprinkle the bread crumbs over the casserole.
Bake in the preheated oven for 25-30 minutes, or until the top is golden and bubbly.
Let the casserole cool for a few minutes before serving. Enjoy!