Preheat oven to 350°. Spray a 13x9 inch baking dish with non-stick cooking spray.
Heat butter and onion in a large skillet over medium heat, 3-5 minutes stirring until onion starts to soften and turn translucent. Add all of the other ingredients (except cheese) and mix until combined.
Pour 1/2 of the chicken mixture into the prepared dish. Sprinkle with half of the cheese. Top with the rest of the chicken mixture. Sprinkle the remaining cup of cheese on top.
Bake covered for 35 minutes until hot and bubbly.