Prepare the sauce by whisking together the ketchup, Worcestershire and soy sauces, mustard and pepper in a small bowl.
Heat the rice bran oil in a wok over a high heat, add the sliced chicken thighs and cook until nicely coloured. Remove the chicken and set aside.
Now add the cabbage, bean sprouts and onion to the wok, and cook until just beginning to brown. Add more oil as need