Preheat the oven to 350°F (175°C).
In a medium saucepan, cook the broccoli in boiling water for about 3 minutes, then drain and set aside.
In a large mixing bowl, combine the cooked rice, shredded chicken, cooked broccoli, cream of chicken soup, milk, garlic powder, onion powder, salt, pepper, and paprika. Mix well until evenly combined.
Transfer the mixture into the prepared 9x13-inch baking dish and spread it out to ensure even cooking.
Top the casserole with shredded cheddar cheese and sprinkle breadcrumbs over the top if using.
Cover the dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 15 minutes or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for a few minutes before serving.