Place half of apples and onions in the bottom of the slow cooker.
Place the roast on top of the apples and onions. Cut slits in the roast about every inch. Insert some of the remaining apple slices in the slits.
season the roast with salt and pepper, then top with the remaining apples and onions. The pour the apple cider around the roast.
Cook on low for 8-10 hours.
Remove pork from slow cooker and allow to rest.
Strain juiced from the slow cooker into a sauce pan. Mix about 1 Tbsp cork starch with 1 Tbsp water and whisk into the cooking juices. Cook over medium heat until thicken. Can use more cornstarch if needed to reach desired thickness.
Shred pork roast and serve with sauce. Serves 6-8.