1Heat oven to 400°F. Spray 9-inch glass pie plate with cooking spray. Sprinkle broccoli, 1 cup of the cheese, the chicken and onion in pie plate.
2In medium bowl, stir remaining ingredients with wire whisk or fork until blended. Pour into pie plate.
3Bake 35 to 38 minutes or until knife inserted in center comes out clean. Sprinkle with remaining 1/2 cup cheese. Bake 1 to 2 minutes longer or until cheese is melted. Let stand 5 minutes before serving.