Crockpot Cheeseburger Supper

In a skillet, brown the ground beef with onions; drain. Place potatoes and seasoning mix in the slow cooker; top with undrained corn and cream of celery soup. Top potato mixture with ground beef and onions; salt and pepper to taste. Dot evenly with ketchup and mustard; top with cheese slices. Cover and cook on low for 7 to 9 hours.
Serves 4.