Combine Italian dressing and fajita seasoning in a shallow dish or zip-top plastic bag; add steak. Cover or seal, and chill 8 hours, turning occasionally. Remove steak from marinade, discarding marinade.
Preheat a two-sided contact indoor electric grill according to manufacturer's instructions on HIGH. Place steaks on grill rack, close lid, and grill 10 minutes (medium-rare) or to desired degree of doneness. Remove steaks, and let stand 5 minutes.
Cut steaks diagonally across the grain into very thin slices, and serve with tortillas, cheese, and Pico de Gallo. Garnish, if desired.
Note: When using an outdoor gas or charcoal grill, grill steaks, covered with grill lid, over medium-high heat (350° to 400°) for 8 minutes. Turn and grill 5 more minutes or to desired degree of doneness. Proceed as directed. For testing purposes only, we used McCormick Fajita Seasoning.