Combine oil, mirin, soy sauce, ginger and garlic in a bowl. Place chicken in a shallow dish. Pour over 1/4 cup of the oil mixture. Set aside for 2 to 3 hours, if time permits.
Cook noodles in a saucepan of boiling water for 4 minutes or until tender. Drain. Rinse under cold water. Set aside.
Preheat a barbecue plate or chargrill over medium heat. Cook chicken for 5 to 6 minutes each side or until cooked through. Remove to a plate. Cover and rest for 5 minutes. Thinly slice.
Place noodles and bok choy on plates. Top with chicken. Drizzle with remaining oil mixture. Serve.