Rinse and pat dry the flank steak. Score the meat lightly in a 5 cm diamond pattern, to allow the flavour of the marinade to penetrate. Combine the remaining ingredients in a flat glass dish or in a heavy ziploack bag. Place meat in the marinade and cover, or seal and marinate in the refrigerator 6 hours or overnight, turning 2-3 times. Preheat the barbecue on HIGH, and brush the grids with oil to prevent sticking. Place the flank steak on hot grids, and reduce heat to MEDIUM. Grill approximately 5 minutes per side for medium. Allow the steak to rest for 3 to 5 minutes before carving. Meanwhile, place the marinade in a small heavy saucepan and bring to a boil on the sideburner or stove and cook for 2 to 3 minutes. Carve the steak into thin slices on the diagonal, against the grain. Drizzle the cooked marinade over the meat.