Combine all the ingredients for the marinade and place in a zip lock bag. Add the flank steak. Marinate several hours or overnight.
Drain marinade and discard.
Grill steak about 5 minutes per side for rare. Transfer steak to platter; let stand 10 minutes. Thinly slice steak across grain.
Note: I now keep my ginger in the freezer. When I need some I grate the amount needed. I try to get my ginger as fresh as possible, thus forgoing the part of having to peel the ginger. I just grate as it. What a snap!