In a very large bowl combine beef, blue cheese, onion, pineapple, ham, bacon pieces, pepper, and garlic powder; mix well. Shape meat mixture into eight 1-inch-thick patties.
For a charcoal grill, place patties on the grill rack directly over medium coals. Grill, covered, for 12 to 14 minutes or until done (160 degrees F to 165 degrees F), turning once halfway through grilling. Top burgers with cheddar cheese. Continue to grill, covered, for 2 minutes more or until cheese is melted. (For a gas grill, preheat grill. Reduce heat to medium. Place patties on grill rack over heat. Cover; grill as directed.) Serve burgers on buns. If desired, top with lettuce, tomato, and onion.