Let pork tenderloin rest at room temperature for at least 30 minutes, but not more than 2 hours, before cooking.
Preheat oven to 220C/425F/Gas 7.
Combine the apple juice and white wine in a small bowl and season with salt and black pepper, to taste. Set aside.
Place a sheet of plastic wrap on a clean, dry work surface. Add the butterflied tenderloins on top of the plastic and cover with a second sheet of plastic wrap. Pound the meat with a meat mallet or rolling pin until it is approximately ⅓”/1cm thick throughout. Season lightly with salt and black pepper.
Heat olive oil in a large skillet or frying pan over medium heat.
Add chopped apples, red onion, and mushrooms. Cook, stirring occasionally until the apples are soft and mushrooms and onion are browned, approximately 8-10 minutes. Season with salt and black pepper, to taste.
Add rosemary, cinnamon, and cloves to the skillet and cook for another 1-2 minutes or until the spices become fragrant. Remove from heat and stir in the chopped dates and crumbled Feta.
Spread the stuffing mixture onto the prepared pork tenderloins and roll up tightly. Secure the roasts with kitchen string or toothpicks.
Carefully transfer the tenderloins to a large roasting pan.
Use a pastry brush to coat the outside of each piece of pork with the apple juice/wine mixture, then pour half of the remaining liquid into the pan.
Sprinkle the pork lightly with salt and black pepper, if desired, before placing the pan into the preheated oven.
Baste the pork with the remaining apple and wine mixture every 10-15 minutes while it cooks. Check for doneness after 50 minutes and continue cooking until an instant-read thermometer inserted into the center of the pork reads just below 145F/63C. (Temperature will increase while the meat rests).
Remove the roasting pan from the oven and cover the pan loosely with foil. Leave to rest for 10-15 minutes before removing the kitchen string or toothpicks.
Slice and serve immediately with a drizzle of pan juices. Enjoy!