Dry the skin of the duck thoroughly and then score it in a cross-hatch pattern (∼1cm or ½" gaps), and set aside (not in the fridge) whilst you prepare the other ingredients.
Peel, then top and tail the onion and cut it into 8 wedges.
Cut the carrot in half lengthways and then cut it into 2-3mm (⅛") thick slices at a 45° angle to the carrot.
Top and tail the runner beans and cut them into 25mm or 1" lengths at a 45° angle.
Peel the garlic cloves and then slice them as thinly as you can.
Peel the ginger and then cut it into batons as thinly as you can.
Slice the spring onions at a 45° angle into strips as thinly as you can.
Mix together the soy sauces, hoisin sauce, shaoxing wine, cornflour and sesame oil in a bowl.
Cook the noodles as per the instructions on the packet and then drain and refresh in cold water.
Place the wok on the hob, then season the duck skin with a pinch of salt, and place the breasts skin side down into the cold wok.
Turn the heat to medium-low and allow the duck to slowly brown for 7-10 minutes. If you are using a ceramic electric hob, this may take a little longer; do not be tempted to turn up the heat.
Flip the duck and cook for another 2 minutes, then remove it and allow it to rest.
Drain off most of the duck fat and add the vegetable oil, then turn the heat up under the wok to high.
When the fat gets really hot, toss in the onion, runner beans and carrot and stir fry for 1 minute.
Add garlic and ginger and stir-fry for another 30 seconds.
Add water chestnuts and bamboo shoots and stir-fry for 30 seconds.
Throw in the bean sprouts and drained noodles and stir fry for 1 minute, then remove the wok from the heat for a minute or two.
Thinly slice the duck breast across the breast; it should still be nice and pink. Add it to the wok, return it to the heat and stir-fry for 1 minute.
Pour in the sauce and cook for 1 final minute.
Toss through most of the spring onions, keeping a few back to sprinkle on top as a garnish.