Set oven control to broil. Spray broiler pan rack with cooking spray. Remove fat from beef. Place beef, mushrooms, squash and onion on rack in broiler pan. Mix dressing, vinegar and pepper; brush over beef and vegetables.
Broil with tops of beef and vegetables 3 to 4 inches from heat 5 minutes. Turn beef; brush dressing mixture over beef and vegetables. Broil about 5 minutes longer or until beef is desired doneness and vegetables are crisp-tender. Discard any remaining dressing mixture. Cut beef into 4 serving pieces. Sprinkle parsley over beef and vegetables.