1Heat oven to 400ºF. Spray 11x7-inch baking dish or 2-quart casserole with cooking spray.
2Spread broccoli in baking dish. Stir Potatoes, Sauce Mix, Cheese Sauce, boiling water and margarine in medium bowl. Stir in milk. Spread over broccoli. Place chicken breast halves on potato mixture.
3Bake uncovered 30 minutes. Place cheese slices on chicken. Sprinkle with Topping. Bake 3 to 5 minutes longer or until cheese is melted and juice of chicken is no longer pink when centers of thickest pieces are cut. Let stand 5 minutes or until sauce is as thick as desired.