Mix together the five spice powder, Szechuan pepper, peppercorns, cumin and the salt and rub onto the meat both inside and outside. Cover with cling film and chill for 24 hours.
Brush the spices off the meat as best you can. Stuff the duck with the ginger and the spring onions and place on an oven-proof plate.
Fill a wok with 5 cm of water and add a steamer insert. Bring the water to the boil and then place the plate of duck onto the steamer insert. Cover and steam the duck on a low heat for around 2 hours. Scoop out the fat every so often and keep topping up the wok with water.
Remove the duck from the wok and drain all the liquid. Remove the ginger and the spring onions from the duck and leave the meat to cool completely. Transfer to the fridge if desired.
To make the salad, wash the bean sprouts in boiling water and drain well. Mix with the cabbage, carrots, apple, chilli, avocado, cucumber, herbs, beans, lime juice and the oil and season with soy sauce and ground black pepper.
Cut the duck into quarters and dust with the potato starch. Heat the peanut oil in a wok or a deep fat fryer. Once the oil begins to smoke, add the duck and fry until crispy. Pat dry with kitchen paper. Remove the meat from the bones and cut into thin strips. Season the salad to taste, arrange on plates with the duck and serve.