Slice and roughly mince the pork belly strips. Don't make it too fine as you want to retain some of the bite and fattiness.
Prepare a tablespoon of ground Sichuan peppercorns. I use a pestle and mortar but you can get it prepared at the Asian supermarket.
Set the wok to medium high heat, add neutral oil and the pork. Cook until it starts to brown then season with light soy sauce, dark soy sauce, Shaoxing wine, ground Sichuan peppercorn, five spice, salt and sugar. Next, add the garlic, white parts of the spring onion and a third of the pack of pickled mustard greens then mix. Once it's crispy, set aside.
Boil your noodles and once cooked, set aside. Use the noodle water to blanche the pak choi.
In a separate bowl, add sesame paste (or tahini), Chinese black vinegar, light soy sauce, chilli oil, ground Sichuan peppercorns, noodle water, sugar and minced garlic and mix well.
Add noodles to the sauce, top with the greens, minced pork and spring onion then enjoy!
