1.Combine chicken, tamari, mirin, ginger and garlic in medium bowl.
2.Place noodles in large heatproof bowl, cover with boiling water; separate with fork, drain.
3.Drain chicken, reserve marinade. Heat half the oil in wok; stir-fry chicken, in batches, until browned. Remove from wok.
4.Heat remaining oil in same cleaned wok; stir-fry onion until softened. Return chicken to wok with reserved marinade; bring to the boil. Add noodles and buk choy; stir-fry until buk choy wilts.
Chicken mixture can be marinated for 30 minutes or overnight.Note