Preheat the oven to 200ºC, fan 180ºC, gas 6. Cut the pork tenderloin in half lengthways, but not all the way through. Open out the pork and bash with a rolling pin until slightly flattened.
Spread with pesto then scatter over the mozzarella. Fold the pork over to close. Lay the prosciutto slices side-by side, overlapping slightly. Place the pork fillet on top and wrap it in the prosciutto.
Place the pork in the middle of a shallow baking tray, putting the carrots and potatoes on one side and the beetroot on the other. Drizzle the vegetables with the oil and season with black pepper.
Cook for 45 minutes, covering the pork with foil for the final 15 minutes of cooking time. To serve, cut the pork into slices and plate up with the vegetables. Drizzle with pan juices and garnish with the parsley.