Preheat oven to 450'. Mix onion, parsley and garlic with ground beef. Press beef mixture evenly over bottom of large stoneware bar pan. Bake 10-12 minutes or until beef is no longer pink.
While beef cooks, cut cheese into quarters and set aside. Slice buns apart neatly at seams (do not separate tops from bottoms). Trim about 1/4 inch from each bun end to square of ends (discard trimmings or save to make bread crumbs for another recipe). Cut buns into thrids for a total of 24 square mini buns; set aside.
Remove bar pan from oven. Pour off juices, if necessary. Cut beef mixture into 24 squares using a pizza cutter. Top each burger with one pickle and one piece of cheese. Place one bun top onto each burger; top with one bun bottom. Cover pan with aluminum foil and bake 3-5 minutes or until cheese is melted and buns are warm.
To serve, place one burger with bun top onto one bun bottom. Repeat with remaining burgers and bun bottoms. Serve immediately.