Preheat grill pan to medium-high. Cook steak about 6 minutes per side, seasoning each side with salt and pepper. In a large bowl, mix tomatoes, onion, and garlic. Let meat rest for 3 to 5 minutes after cooking, then slice across the grain and diagonally into thin strips. Add meat and lettuce to bowl, pour on vinaigrette and toss well so that everything is completely coated. Top with cheese.