Rub 2 teaspoons garlic and pepper over steak. Grill over medium-hot heat on a covered grill 3 to 5 minutes per side for medium doneness depending on thickness of steak. Transfer steak to a carving board; tent with foil and let stand 5 minutes.
Meanwhile, combine lettuce, tomato, avocado, 1 cup cheese and red onion in a large bowl. Combine oil, lemon juice and remaining garlic in a small bowl; mix well. For a spicier dressing, add chipotle chilies. Add mixture to bowl; toss with lettuce mixture. Transfer to four serving plates.
Carve steak crosswise into thin slices; arrange over salads. Top with remaining cheese.