Marinate the steak in the ingredients above for 4-6 hours. 30 minutes prior to grilling, remove steak from refrigerator and let sit at room temperature.
Grill to medium-rare (about 3 min each side). Since the thickness of skirt steaks can vary, make sure that you put the thicker slices on the grill first.
Let the cooked steaks rest for 5 minutes. Slice ACROSS the grain into thin slices.