Pat the pork loin dry with paper towels. Season it all over with 1/2 teaspoon of salt and 1/4 teaspoon of pepper.
Heat the olive oil in a large skillet over medium-high heat. Carefully place the pork in the skillet and sear for 2-3 minutes per side, until browned all over. Transfer the seared pork to a plate.
While the pork sears, dice one of the apples. Leave the other apple for slicing.
Spread the cubed sweet potato, diced onion, and diced apple in the bottom of a 6-quart slow cooker. Sprinkle with the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper and toss to combine.
Slice the second apple into thin wedges. Cut several slits into the top of the seared pork loin, about 1/2 inch deep. Gently push the apple slices into the slits.
Place the pork loin on top of the vegetable and apple mixture in the slow cooker.
Drizzle the honey over the pork and apples, then sprinkle everything with the cinnamon.
Cover and cook on LOW for 4 to 5 hours, or on HIGH for 2 to 3 hours. The pork is done when it is tender and a meat thermometer inserted into the thickest part reads 145°F (63°C).
Remove the pork from the slow cooker and let it rest on a cutting board for at least 3 minutes before slicing. Serve with the cooked apples and vegetables.