Preheat oven to 200C/400F/Gas 6.
Place the pork loin between two pieces of cling film. Flatten out the pork with a meat mallet or the end of a rolling pin, until 1cm/¼in thick.
Place the chopped pistachios onto a clean flat surface. Press one side of the pork onto the pistachio nuts, to coat, and season with salt and freshly ground black pepper.
Heat the olive oil and butter in a frying pan, add the pork, apple wedges and the sweet potato and fry until the pork is golden-brown on the underside. Transfer the pork to a baking tray and place into the oven to roast for five minutes, or until completely cooked through.
Meanwhile, continue frying the apples and sweet potato, until cooked through and golden brown.
To serve, place the pork in the centre of a plate with the apples and sweet potato arranged around it.