Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish with cooking spray or butter.
In a large mixing bowl, combine the cooked rice, broccoli florets, cheddar cheese, cream of mushroom soup, milk, garlic powder, onion powder, black pepper, and salt. Mix until well combined.
Pour the mixture into the prepared baking dish and spread it evenly.
In a small bowl, combine the breadcrumbs and melted butter. Stir until the breadcrumbs are evenly coated.
Sprinkle the breadcrumb mixture over the top of the casserole.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is golden brown.
Remove from the oven and let it cool for 5 minutes before serving.