Mix beef with the onion, parsley, salt, pepper, Worcestershire sauce and garlic. Shape into pattie. Brush lightly with olive oil and grill until desired doneness.
Meanwhile, toast bun and spread mustard on bottom half. Warm onion and cook bacon.
Put burger on bottom half of bun, top with onions and Swiss. Melt cheese under a broiler.
Top with tomato slice, lightly seasoned with salt and pepper. Top with bacon and Sharp Cheddar. Melt cheese under a broiler, top with bun.