Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the cooked rice, shredded chicken, broccoli florets, ¾ cup of shredded cheddar cheese, cream of mushroom soup, milk, garlic powder, onion powder, black pepper, and salt. Mix well to combine all ingredients evenly.
Transfer the mixture into a greased 9x13 inch baking dish, spreading it out evenly.
If using, sprinkle the remaining ¼ cup of cheddar cheese and bread crumbs over the top of the mixture for a crunchy topping.
Cover the baking dish with aluminum foil (if desired) and place it in the preheated oven.
Bake for 30 minutes, then remove the foil and bake for an additional 15 minutes, or until the casserole is bubbly and golden on top.
Once cooked, remove from the oven and let it rest for 5-10 minutes before serving.