In a glass dish or large sealable plastic bag, combine the chili paste, sesame oil, soy sauce, brown sugar, sesame seeds, ginger and garlic. Add the onion and meat and stir gently. Cover the dish or seal the bag and let marinate for 2 hours in the refrigerator.
Preheat a cast iron grill pan until very hot. Oil the pan. Grill a third of the meat and onion at a time until marked on both sides. Add oil, if needed. Garnish with the green onions and serve wrapped in lettuce leaves.