Prepare outdoor grill for direct grilling over medium-high heat. Brush both sides of steaks with oil and season with salt and pepper. Transfer steaks to grill and cook 4 minutes or until golden brown. Flip steaks and cook 5 to 7 minutes longer or until internal temperature of steaks reaches 140 degrees F for medium doneness.
Transfer steaks to cutting board and loosely tent with foil. Let rest 5 minutes, then thinly slice.
Divide steak between lettuce leaves. Top with onion, cheese, tomatoes and jalapeño, if using. Serve immediately.