Lightly score the top of the flank steak in a crosshatch pattern, being careful not to cut too deeply into the meat.
In a large ziplock bag, or a shallow pan large enough to fit the steak, whisk together all the remaining ingredients. Place the steak in the marinade and coat all over with marinade. Refrigerate steak for at least 4 hours, or up to 8 hours.
Preheat the grill. Remove steak from marinade and dispose of the extra marinade. Grill the steak until medium rare, about 5 minutes a side, and the internal temperature is about 125 degrees. Remove from heat and let rest for at least 10 minutes. Slice steak in very thin slices across the grain.