Place pork, green onions and water chestnuts in a 5-qt slow cooker. Mix hoisin sauce, soy sauce, sherry, garlic, gingerroot, corn syrup, marmalade, pie spice and pepper flakes in a bowl. Pour over pork. Cook, covered, on low until meat is tender, 6-8 hours., Remove to a serving platter; keep warm. Skim fat from cooking juices; transfer to a small saucepan. Bring to a boil. Mix cornstarch and water until smooth. Gradually stir into saucepan. Bring to a boil; cook and stir until thickened, about 2 minutes. Serve with ribs, rice and, if desired, additional green onions.