Prep Time: 10
Cook Time: 10
Serves: Serves: 4
Prepare grill, preheat broiler or have a grill pan ready to preheat. Combine meat, onion, salt, pepper and 3 tablespoons mustard; mix well. Shape to form 4 oval patties about 1/2-inch thick.
Grill patties, covered, over medium-hot coals or broil 4 inches from heat source or cook in a hot grill pan over medium-high heat 5 minutes per side or until no longer pink in center. Arrange cheese attractively over patties; continue cooking until cheese melts, about 1 minute.
Place patties on bottoms of buns; top with lettuce and tomato. Spread remaining 2 tablespoons mustard over insides of bun tops; close sandwiches.