Shape beef into 12 thin patties. Top six patties with a slice of cheddar cheese, green pepper strips and a slice of onion, tomato and Swiss cheese. Top each with another patty and seal edges. Season to taste.
Grill beef, covered, over medium heat or broil 4 in. from the heat for 4-5 minutes on each side or until a thermometer reads 160° and juices run clear. Serve on lettuce-lined buns. Yield: 6 servings.