In a large bowl beat egg slightly. Add oats, catsup, salt and pepper and mix well. Mix in ground beef.
Shape into a loaf and place in an 8 by 4 inch loaf pan. Bake for 1 hour and 15 minutes.
Remove meatloaf from oven, cool a bit. Remove from pan and drain. Place on a large oven proof pie plate or serving plate. "Frost" or cover meatloaf on sides and top with mashed potatoes. Bake for 15 minutes more.
Sprinkle cheese on top and return to hot oven until cheese is melted. Slice and serve.