Preheat the oven to 200 degrees C. Put the pork fillets on a chopping board and cut each in half lengthways, without cutting all the way through. Open the fillets like a book and press down to flatten slightly.
Finely grate the zest from the orange and set aside. Using a small, serrated knife, cut away all the white pith from the orange, then slice down between the membranes to remove the orange segments. Arrange the orange segments over the cut surface of one fillet. Top with the sliced prunes and ginger, sprinkle with the orange zest, then season to taste.
Place the second fillet, cut-side down, on top and gently press the fillets together. Wrap the bacon rashers around the pork and secure in place with kitchen string. Set aside.
Spread the potatoes over the base of a large roasting tin, then scatter over the leeks and carrots. Core and thickly slice the apples, then add to the tin. Place the pork-fillet package on top and pour in the cider. Roast for 1 hour or until the potatoes and carrots are tender and clear juices come out of the pork when it is pierced with the tip of a knife. Lift out the pork and vegetables, cover with foil and leave to rest and keep warm for 10 minutes.
Meanwhile, put the roasting tin on the stove and boil the cooking liquid over a high heat until it is reduced to about 2/3 cup (170ml). Add the parsley and season to taste. Slice the pork and serve with the vegetables and the cooking juices spooned over the top.