Cook and stir ground beef and onions in large skillet for 4 to 5 minutes. Add steak sauce; heat to a boil. Reduce heat and simmer for 5 to 7 minutes. Spoon into 1 1/2-quart casserole.
Mix mashed potatoes and cheese. Spread mashed potato mixture evenly over beef mixture.
Bake at 350° F for 12 to 15 minutes or until heated through.Servings: 4