Diagonally slash outer edge of fat at 1-inch intervals to prevent curling (do not cut into lean). Marinate beef as directed on envelope of meat marinade.
Mix sugar, cornstarch, mustard and salt in 1 1/2 quart saucepan. Stir in water, orange peel, orange juice and lemon juice. Cook, stirring constantly, until mixture thickens and boils. Boil and stir 1 minute.
Set oven control to broil and/or 550 degrees. Place beef on rock in broiler pan. Broil with top 2 to 3 inches from heat until brown, about 8 minutes.
Brush with orange sauce; turn. Broil until desired doneness, 8 to 10 minutes for medium.
Brush with orange sauce; sprinkle with onions Serve with sauce.