Preheat your oven to 375Β°F (190Β°C). Grease a 9x13 baking dish.
π₯£ In a large skillet, melt butter over medium heat. Whisk in flour and cook for 1-2 minutes. Gradually add milk, whisking until smooth.
π§ Stir in garlic powder, onion powder, salt, and pepper. Cook until the sauce thickens, then mix in cheddar cheese until melted.
Combine chicken, cooked rice or pasta, and broccoli (if using) in a large mixing bowl. Pour the cheese sauce over the mixture and stir to combine.
Spread the mixture evenly in the baking dish.
π§ For the topping, mix breadcrumbs with melted butter. Sprinkle mozzarella, parmesan, and the breadcrumb mixture evenly over the casserole.
Bake uncovered for 25-30 minutes, or until the top is golden and bu