1Move oven rack to position slightly above middle of oven. Heat oven to 500ºF.
2Generously spray rectangular pan, 13x9x2 inches, with cooking spray. Place baking potatoes, sweet potato and onions in pan. Mix dressing and red pepper; pour over vegetables. Cover and bake 10 minutes.
3Stir bell pepper into vegetables. Cover and bake 5 minutes; stir vegetables. Bake uncovered 10 minutes longer.