Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the cooked rice, broccoli florets, shredded chicken, cream of mushroom soup, milk, garlic powder, onion powder, salt, and black pepper. Mix well until all ingredients are evenly coated.
Stir in 1 cup of shredded cheddar cheese, reserving the remaining cheese for topping.
Pour the mixture into a greased 9x13 inch baking dish, spreading it evenly.
If using breadcrumbs, sprinkle them on top of the casserole for added crunch.
Top the casserole with the remaining ½ cup of shredded cheddar cheese.
Bake in the preheated oven for 35-45 minutes, or until the casserole is hot and bubbly, and the cheese is melted and slightly golden.
Remove from the oven and let it cool for a few minutes before serving.