Whisk all ingredients, except for the steak, in a small bowl.
Place the flank steak into a gallon sized resealable plastic bag. Pour the marinade over the steak and press to remove all air and seal. Refrigerate for at least 3 hours.
Set all burners of a gas grill to medium. Grill 5 minutes per side. Let the beef rest for 15 minutes before slicing thinly, against the grain.