Have a large wok or frying pan hot over a high heat Add the oil to the pan followed by the chicken and fry for a minute, tossing to coat in the oil and to color on each side. While the chicken is cooking grate the ginger, thinly slice the celery and add to the chicken, cook for another minute.
Roughly chop the bok choy and add it to the pan along with the hoisin sauce, ketchup, soy and Chinese five-spice. Add a splash of water and cook, stirring, for another minute. Serve with a sprinkle of coriander leaves