Wash potatoes and cut in cubes. Cut onion into pieces. Tear 6X6 inch foil wrap square for each serving. Take ¾ cup of potato and a ¼ cup of onion and place in the center of each sheet of foil along with peppers if desired. Sprinkle with Spud Rub. Dot with butter or drizzle with oil. Pull the corners of the foil together to seal. Place in a hot oven or on a hot grill and cook approximately 25 minutes or until the potatoes are tender. Serve one foil packet per person. NOTE: Great cooked in an open campfire as well!!