Debone and take off the skin of the chicken. Cut into small bite size pieces.
Prepare the vegetables and mushrooms for a stir fry by having them sliced.
If you are using dried shiitake mushrooms, soak it in water for 2 hours to overnight.
In a large bowl combine all the ingredients for the sake sauce; shoyu, chicken stock, sake, and sugar.
Cover and marinate place the chicken in the sake sauce for 30 minutes to 24 hours in the fridge.
Bring a large pot of water to a rolling boil. Add in the bean thread noodles and let it cook for 5 minutes or until it has become translucent. Drain and set aside.
In a pot or large wok, add in the oil. Let the oil heat up over medium heat. Add in the crushed ginger. Fry until fragrant. Add in the marinated chicken while keeping the sake sauce on the side for later use. Stir fry the chicken until all has been browned.
Add the prepared vegetables to the wok; onions, carrots, and celery. Stir fry for about a minute or two.
Add in the sliced bamboo shoots, watercress, and shiitake mushrooms. Fry for another minute or two.
Add in the sake sauce and let it simmer for five minutes. Then add in the noodles and mix it into the veggies and sauce. Lastly add in the green onions and stir it into the dish.
Remove from the heat and serve immediately and enjoy!