Roll the meat in the curry powder, add vinegars and set aside to marinate for 3-4 hours.
Heat the oil in an ovenproof dish on a hot plate, stir in the onions and cook over medium heat until transparent. Add the marinated meat, stirring well to combine with onions.
Heat through, then place in a slow oven 150 degrees C for 30 minutes.
Test for salt and chilli heat, and adjust to taste. Add sugar, and water if necessary, then return to oven for a further 30 minutes or more, until pork is tender.