Cut steak into thin slivers and put in a bowl. Add soy sauce, sherry, ginger, garlic, five-spice powder and chili sauce. Mix well, then cover and marinate in refrigerator for 1 hour, stirring occasionally. Heat oil in a large frying pan or wok. Add onion and red pepper and stir-fry for 1 minute.
Add beef mixture to pan and stir-fry for 2-3 minutes, stirring all the time. Turn mixture into a warm serving dish. Serve at once with chilled lettuce cups, garnished with sprig of parsley. To serve, simply spoon beef mixture into lettuce cups and eat with the fingers. Serve with plenty of napkins or finger bowls - it can be a little messy.