Cut the chicken breasts into strips, lay in a bowl and sprinkle with soy sauce and freshly ground black pepper. (Do not add salt as the soy sauce is already salted.) If you have time leave them to marinade for between 10 minutes to 24 hours.
Heat the oil in a wok or deep frying pan. Seal the chicken for 2-3 minutes.
Add the carrots, onions, peppers (Ben used a little of each coloured pepper) and leeks and continue to stir fry for another 4 minutes.
Add the sliced mushrooms, bean sprouts and water chestnuts (if using) and fry for another 2-3 minutes.
Tip the remaining marinade into the pan for extra flavour.
As soon as the meat is cooked through serve on a bed of boiled rice. The vegetables should retain some crunch.
To ring the changes, instead of serving this dish with rice, why not try quinoa?