Put the strips of chicken in a bowl. Mix together the hoi sin sauce, soy sauce, coriander and garlic and pour over the chicken, turning the pieces over until they are well coated. Cover the bowl with cling film and leave to marinate in the fridge for several hours or until ready to cook.
Heat 2tbsp of the oil in a wok or large frying pan and stir-fry the red onion for 3 minutes. Add the carrot, stir-fry for 2 minutes, then add the courgette and mushrooms and stir-fry for 3 minutes. Tip the vegetables out of the pan on to a plate and set aside.
Add the remaining tablespoon of the oil to the pan. Lift the chicken out of the marinade and stir-fry for 2 minutes. Add the beansprouts, stir-fry for 1 minute, then return the vegetables to the pan.
Toss everything together over the heat for 1-2 minutes until piping hot. Serve at once with noodles or rice.