Preheat your oven to 375°F (190°C).
In a large mixing bowl, combine the cooked chicken, broccoli florets, and cooked rice.
In a separate bowl, whisk together the cream of chicken soup, milk, sour cream, garlic powder, onion powder, salt, and pepper.
Pour the creamy mixture over the chicken, broccoli, and rice. Add 1 1/2 cups of the shredded cheese. Stir gently to combine all ingredients.
Transfer the mixture to a greased 9x13 inch casserole dish, spreading it evenly.
Sprinkle the remaining 1/2 cup of cheese over the top.
Bake for 25-30 minutes, until the cheese is melted and bubbly.
If desired, top with crispy fried onions and bake for an additional 5 minutes.
Let the casserole cool for 5-10 minutes before serving.