Mix dressing, 4 tablespoons steak sauce, sugar, and garlic until well blended. Pour over steak in shallow dish; turn steak to coat both sides. Refrigerate 1 hour to marinate.

Heat oil in a large skillet on medium-high heat. Add onions; cook and stir 5 minutes. Cover; cook on medium-low heat for 15 minutes or until onions are golden brown, stirring occasionally.

Meanwhile, heat broiling pan under broiler. Remove steak from marinade; discard marinade. Place steak on broiler pan. Broil steak 4 inches from heat, 6 minutes on each side or until cooked to Medium center. Remove from heat; cover. Let stand 5 minutes before cutting across the grain into thin slices. Stir Worcestershire sauce into onions and cook 1 minute more. Serve over steak.