Preheat oven to 400°.
Brown ground beef with onion in 12-inch nonstick skillet over medium-high heat, stirring occasionally; drain, if desired. Remove skillet from heat, then stir in relish and ketchup. Season, if desired, with salt and ground black pepper.
Evenly spread ground beef mixture in 8-inch glass baking dish, then top with Shedd's Country Crock™ Side Dishes Homestyle Mashed Potatoes and cheese. Bake 15 minutes or until heated through. Let stand 10 minutes before serving. Garnish with lettuce, tomato and onion.