Trim the tenderloin of all fat and sinew, then cut into 12 medallions. Put the pork pieces between two pieces of clingfilm, and bash them so they are about 1cm thick. Season both sides. Heat 1 tsp oil in a non-stick frying pan, and fry the pork for 2 minutes on both sides, until golden and cooked through. Scoop out of the pan, then stir-fry the peppers, onions and garlic in another tsp oil for 5 minutes, then add the stock and the thyme sprigs. Add a lid or a sheet of baking paper and simmer for 10-15 minutes until the peppers are soft. Add the vinegar and paprika and season. Fry for another 2 minutes with the lid off, stir in the pork pieces (with any resting juices) to warm in the stew for a minute. Scatter with parsley and serve with white bean mash or brown rice.