Preheat the oven to 425 degrees . Place the pork on one side of a large baking dish, rub with 1 tablespoon olive oil and season with salt and pepper. On the other side of the dish, combine the lemon, onion, 1 tablespoon olive oil and the sugar; season with salt and pepper and arrange in an even layer. Roast until the pork registers 150 degrees on an instant-read thermometer and the lemon slices are browned around the edges, about 30 minutes. Tent the pork with foil and let rest.
Transfer the lemon mixture to a work surface and chop. In a medium glass bowl, combine the apple juice and raisins; microwave on high power for 1 minute. Stir in the lemon mixture, apple, vinegar and the remaining 1 tablespoon olive oil and season with salt and pepper. Thinly slice the pork and serve with the relish.