Preheat your oven to 350°F (175°C).
In a large pot, bring water to a boil and blanch the broccoli florets for about 2-3 minutes until they are bright green. Drain and set aside.
In a mixing bowl, combine the cooked rice, cooked chicken, blanched broccoli, cream of chicken soup, milk, 1.5 cups of shredded cheddar cheese, garlic powder, onion powder, salt, and pepper. Stir well until all ingredients are mixed thoroughly.
Transfer the mixture into a greased 9x13 inch casserole dish. Spread it out evenly.
Sprinkle the remaining 0.5 cup of shredded cheddar cheese on top. If using breadcrumbs, sprinkle them over the cheese for added crunch.
Cover the casserole dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Allow to cool for a few minutes before serving.