Combine marinade ingredients in small bowl; mix well. Place beef steak and marinade in food-safe plastic bag; turn steak to coat. Close bag securely and marinate in refrigerator 6 hours or as long as overnight.
Remove steak from marinade; discard marinade and salt to taste. Place steak on grid over medium, ash-covered coals. Grill flank steak, uncovered, 17 to 21 minutes for medium rare to medium doneness (top round steak 16 to 18 minutes for medium rare doneness; do not overcook), turning occasionally. Carve steak across the grain into thin slices.