Boil (or poach) the chicken for 20 minutes. Heat a lightly greased wok, and add the Chinese leeks thinly sliced into 2- to 3-inch pieces. Cook through and set aside. Heat the wok again, and add crushed garlic. Let cook until fragrant, about 30 seconds to 1 minute, then add chopped chicken pieces with 1 tablespoon soy sauce, 1 tablespoon rice wine vinegar and a pinch of sugar. Add the cooked leeks and heat through for a few more minutes before serving.