Mix together the pork marinade ingredients in a bowl. Put the pork in a high sided roasting dish and pour over the marinade. Leave for at least 1 hour, or up to 48 hours.
Preheat the oven to 100 degrees Celsius.
Pour the excess marinade from the roasting dish into a small saucepan. Put on a low heat and simmer until it thickens, then turn off the heat. Meanwhile, put the pork in the oven for 2 hours 30 minutes. Every 30 minutes, remove from the oven and brush with some of the thickened marinade. Remove from the oven, cover with foil and rest for one hour.
Boil the kettle. Put the udon noodles into a large bowl and cover with the boiling water. Soak for 5-10 minutes, then drain.
For the lo mein, heat the oil in a wok over a high heat. Add the garlic and ginger and cook for 2 minutes.
Cut the broccoli, mushrooms and choi sum into 1-2 inch pieces and add to the wok. Cook for 5 minutes, stirring constantly.
Tip in the shaoxing wine. Let it bubble up, then add the noodles, oyster sauce and soy sauce. Cook for another 3-4 minutes, stirring continuously.
To serve, spoon the lo mein into bowls and top with the sliced pork.