Make the sauce. In a small mixing bowl, mix together the cornstarch and dark soy sauce until lump free. Then mix in the light soy sauce, oyster sauce, shaoxing wine, brown sugar, toasted sesame oil, salt and white pepper.
Season the chicken. Cut the chicken into 1/2 inch slices. In a medium sized mixing bowl, toss the chicken with 1 tablespoon of the sauce to marinate for about 30 minutes. Set aside.
Prepare the noodles. Cook the noodles in boiling water according to the instructions on the package. If using fresh noodles, cook for about 30 seconds- 1 minute.
Stir fry the onion and garlic. Heat a 1-2 tablespoons of vegetable oil in a wok or large skillet over high heat until hot. Add the onion and garlic and stir fry until lightly browned and translucent.
Toss in the marinated chicken for about 2 minutes until lightly cooked Toss the chicken using two wooden spoons until the chicken is white on the outside.
Toss in the vegetables. Next toss in the carrot and bell peppers and stir fry for about 2 minutes. Then add in the mushrooms and snow peas and toss for an additional 1 minute. Lastly toss in the napa cabbage and toss until wilted another 2 minutes.
Add the noodles, sauce and green onion. Toss in the noodles, sauce, water and continue tossing together for an additional minute. Add the green onions and toss until the green onion is softened and the noodles are evenly coated with sauce. (Optional: for a spicy chicken lo mein, toss with chili oil or sriracha)
Enjoy! Serve immediately.