Preheat oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a saucepan, bring 2 cups of water to a boil, then add instant rice and cook as per package instructions.
Steam or microwave the broccoli until tender.
In a large bowl, mix chicken, cooked rice, broccoli, cheese, cream of mushroom soup, cream of chicken soup, milk, butter, and chopped onion.
Stir everything together until well combined, then spread the mixture evenly in the prepared baking dish.
Bake for 25-30 minutes or until the cheese is bubbly and golden on top.
Let it cool for a few minutes before serving.
Enjoy warm with Mashed Potatoes or Cottage Cheese Flatbread for a complete meal!