In a food processor, combine the garlic, cilantro stems, salt, pepper, and two tablespoons oil. Spread the paste on both sides of the lamb and marinate for 30 minutes. Warm remaining oil in a large, heavy skillet, cooking the steak or chop on each side 5–6 minutes for medium-rare. Remove from pan and let cool. For the salad, cut the lamb into strips. Divide the lettuce leaves among 4 plates and arrange the mango, avocado, greens, and strips of lamb on top.