Heat the oil in a frying pan and add the pork; cook until browned, then remove from the pan.
Add onion, garlic, ginger, garam masala and mustard seeds to the same pan. Cook until onion is soft, about 5 minutes.
Return the pork to the pan and add vindaloo paste and cook, stirring for 2 minutes. Add about a pint of water and bring to the boil. Reduce heat and simmer, covered until meat is tender, about 1 to 1 and a half hrs. Check and add more water if sauce is getting too thick. Serve with naan bread, chappati or basmati rice. Enjoy!