Preheat oven to 425 F. Slice bun tops into 1/4 inch strips (if buntops are very thick, slice bottoms off horizontally before slicing into strips). Arrange in a sinle layer on cookie sheet; bake 8-10 minutes or until lightly toasted. Remove to cooling rack; cool completely.

Slice half of the onion crosswise into thin rings. Reove and discard stems from tomatoes; cut tomatoes into qarters lengthwise and slice crosswise. Set onion and tomatoes aside.

Cook ground beef in saute pan or skillet over medium-high heat until no longer pink, breaking beef into crumbles. Chop remaining onion half. Finely dice pickles. In medium bowl, combine chopped onion, pickles, ketchup and mustard. Add cooked ground beef; mix well.

To serve, arrange lettuce on large serving platter. Spoon beef mixture over lettce. Top with cheese, tomatoes and sliced onion. Arrange hamburger bun croutons around edge of platter. Serve immediately.