Put the chicken in a glass or ceramic bowl, add the soy sauce and toss well to coat. Cover and leave to marinate in a cool place for 10 minutes.
Heat the oil in a wok or large frying pan, add the chicken and marinade and stir-fry for 2 minutes. Add the carrots and peppers and stir-fry for 4 minutes. Add the sauce and spring onions and cook briefly, stirring, to heat through. Serve immediately over egg noodles.