Preheat the oven to 400 degrees F.
Season the pork loin with cinnamon, salt, and pepper. You can mix the three ingredients in a small bowl and then sprinkle it together on the top of the loin.
Slice the apples an onion in ¼ inch slices. Spread them out on the bottom of a baking dish that is large enough to hold the pork loin (about 9×13-inch).
Add the pork loin on top of the apples and onions with the fat side up in the baking dish. Top the meat with a few of the apple slices.
Squeeze the juice of two oranges around and on top of the pork.
Drizzle the pork with honey then add fresh rosemary leaves diced on top (about 1 tablespoon) or add sprigs to the sides.
Bake for 55-60 minutes or until the internal temperature reaches 140 degrees F. It will continue to cook once removed from the oven about 5 to 10 degrees more as it sets. Use a meat thermometer to make sure the pork is cooked to a safe temperature. It is safe to eat when it reaches at least 145 degrees F in the center.
The pork will continue to cook slightly once it is removed from the oven, so it is important not to overcook the meat. Remove it at 140 degrees F., cover and recheck with a meat thermometer in a few minutes. It will be juicy and tender.