Marinate mushrooms for 30 minutes in Worcestershire sauce (reserving 1 tablespoon).
Combine mayonnaise, remaining Worcestershire, mustard, parsley, and 1/2 teaspoon pepper.
Remove mushrooms from marinade (discard unused marinade) and grill; slice mushrooms.
Form ground chuck into 4 patties. Season with salt and pepper and grill. Just before desired doneness is reached (recommended 160°F internal temperature), top burgers with cheese and grill until cheese melts.
Generously spread bun with flavored mayonnaise, top with burgers, red onion, mushrooms and bacon.
Recipe and photo courtesy of Certified Angus Beef.