01 - Preheat oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with butter or non-stick spray.
02 - Blanch broccoli florets in boiling water for 2–3 minutes and drain if using fresh. If using frozen, thaw and pat dry.
03 - In a large mixing bowl, combine cooked chicken, rice, broccoli, 1½ cups of cheddar cheese, cream of chicken soup, milk, onion powder, garlic powder, salt, and black pepper. Mix well to combine.
04 - Evenly spread the combined mixture into the prepared baking dish. Top with remaining ½ cup cheddar cheese and sprinkle breadcrumbs over the top, if using.
05 - Transfer dish to the oven and bake for 25–30 minutes until hot, bubbly, and the cheese topping is golden and melted.
06 - Allow casserole to rest for 5–10 minutes before serving to help the flavors set.