Preheat the oven to 200°C.
Cut one of the apples into thick slices and arrange them in the base of a roasting dish.
In a small bowl, mix the cinnamon, ginger, marjoram (or oregano) and olive oil. Brush the pork all over with this spiced oil and season with salt.
Place the pork on top of the apple slices and roast for about 20 minutes, or until the skin begins to crisp and turn crackly.
Meanwhile, cut the remaining apple and the onion into wedges.
Remove the roasting tray from the oven and lower the temperature to 180°C.
Add the apple juice to the tray along with the apple and onion wedges. Brush them lightly with any remaining spiced oil and season with salt and pepper.
Return the tray to the oven and roast for about 1 hour (roughly 20 minutes per 500g), or until the pork is cooked through and tender.
Once done, transfer the pork, apples and onions to a serving plate and let them for about 20 minutes.
Use the cooking juices in the tray to make a simple gravy if you like.
Carve the pork and serve with the roasted apples, onions, gravy and your favourite side dishes.