1. Combine all ingredients in a large shallow baking dish. Add steak, turning to coat. Cover and marinate steak in the refrigerator, 45 minutes.
2. Meanwhile, heat grill. Remove steak from refrigerator and let stand at room temperature, 15 minutes. Remove steak from marinade and grill 5 minutes. Turn and grill steak 3 to 5 minutes more, or until an instant-read meat thermometer inserted in center of steak registers 135 degrees F for medium-rare. Transfer to cutting board and slice. Divide and fill warm tortillas with steak, Pico de Gallo and sour cream, if desired. (Nutrition facts are based on per serving without Pico de Gallo or Sour Cream.)