1. Cook the noodles for 3 minutes in a pan of boiling water until al dente, or as per the package instructions. Drain, then run them under cold running water, and drain again. Drizzle with a few splashes of sesame oil, and toss through to prevent them from sticking.
2. Season the chicken with a splash of dark soy sauce, the five-spice powder, and chilli sauce, if using. Mix well.
3. Coat the chicken breasts lightly with the cornstarch. Heat a wok over a high heat, add the groundnut or peanut oil, and heat until smoking. Then, add the chicken, and stir-fry for 2 to 3 minutes, or until cooked through.
4. Add the red pepper, and stir-fry for 1 minute, then add the bean sprouts and green onion and stir-fry for less than 1 minute. Add the cooked noodles, and season with the light soy sauce, 1 teaspoon toasted sesame oil, and black pepper, to taste.
5. Stir well and serve immediately.