Source: Cindy5_NY, she found it from yahoo answers, I adapted it a bit!
adapted by http://theresalwaysthyme.blogspot.com/
3 pounds skirt steak (cut in 1/2 pound pieces)
3 cloves garlic, cut in half
fresh ground black pepper
2 small onions or a few shallots, sliced
oil for sauteing
Rub both sides of steak with cut side of garlic. In a large ziploc bag, pour in some Worcestershire Sauce, a little salt, some pepper, the garlic and the sliced onions. Let marinate for a few hours in the refrigerator, or at room temperature for an hour.
Add oil to frying pan, heat pan to medium or medium-high heat. When hot, add steak and the onions and sear a few minutes on each side, depending on desired doneness.