Combine stir-fry sauce, sherry and cornstarch; set aside.
Stir-fry pork, onion and garlic together in hot wok or large skillet over high heat until pork is no longer pink; drain excess fat. Add stir-fry sauce mixture; cook, stirring, until pork is evenly coated with sauce. Remove from heat; stir in cilantro and sesame oil. To serve, place desired amount of meat mixture in lettuce leaf and wrap to enclose.