1Heat oven to 400°F. Spray 13x9-inch (2-quart) glass baking dish with cooking spray. Sprinkle chicken, onion, bell pepper and broccoli in baking dish.
2In medium bowl, mix remaining ingredients except Cheddar cheese until smooth; pour over chicken mixture.
3Bake 20 to 25 minutes or until knife inserted in center comes out clean. Sprinkle with Cheddar cheese. Bake 3 to 5 minutes longer or until cheese is melted. Let stand 5 minutes before serving.