In a large bowl, combine all marinade ingredients and mix well. Add beef strips, stir thoroughly with marinade. Cover and refrigerate for 3 hours or overnight.
Heat half the cooking oil in a wok over high heat; stir-fry undrained marinated beef in batches, until beef is browned all over and just cooked through. Remove from wok.
Heat remaining cooking oil in wok. Stir-fry mushrooms, choy sum stalks, spring onions and water. Cover and cook for 3-4 minutes or until vegetables are tender.
Return beef to wok. Add Lee Kum Kee Hoisin Sauce, choy sum leaves, rice wine and Lee Kum Kee Premium Soy Sauce; stir-fry until choy sum leaves just wilt. Serve stir-fry topped with extra sliced chilli.