Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C).
Bring water to a boil in a medium saucepan; stir in rice, cover, and remove from heat. Let stand for 5 minutes.
Combine prepared rice, chicken, broccoli, processed cheese, mushroom soup, chicken soup, milk, butter, and onion in a 9x13-inch baking dish.
Bake in the preheated oven until cheese is melted, about 30 to 35 minutes, stirring halfway through cooking to help cheese melt evenly.
