Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish lightly with butter or nonstick spray.
In a medium saucepan over medium heat, bring 2 cups water to a boil.
Add the rinsed 2 cups instant rice to the boiling water, stir once, and cook for about 5 minutes, or until the water is absorbed. Remove from heat and fluff the rice with a fork.
In a large mixing bowl, combine the cooked rice, drained canned chicken, cream of mushroom soup, cream of chicken soup, milk, butter, thawed broccoli, chopped onion, and cubed Velveeta cheese. Stir until uniform and creamy.
Transfer the mixture to the greased baking dish, spreading evenly. Cover loosely with foil if you prefer a softer top.
Bake for 30 minutes, or until the cheese is melted and the casserole is heated through. Remove foil during the last 5–10 minutes for a golden top.
Let the casserole cool slightly before serving.
Notes
Store leftovers in an airtight container for up to 3–4 days. This casserole freezes well; cool completely before freezing.