Heat the oven to 170ºC (150º fan) 350ºF, gas 3.
Score the skin of the pork. Mix together the oil, mustard, chilli powder and Worcestershire sauce, season with salt and pepper and rub the mixture into the pork. Place in a roasting tin, cover with foil and roast in the oven for 3 hours or until the pork is meltingly tender.
Let the meat cool a little then pull the flesh into shreds using two forks.
Mix together the onion, cabbage, carrot, scallions and lemon juice. Spread the bread rolls with butter and make sandwiches with the pulled pork and the vegetables.