Place the flank steak in a shallow bowl. In a separate bowl, combine the rest of the ingredients and whisk until blended. Pour the marinade over the steak — make sure the meat is completely covered. Cover the bowl and allow the beef to marinate in the fridge for about an hour. On a lightly oiled grill set to high heat, cook the beef until it's charred and completely cooked through. This should take about 1 or 2 minutes on each side.