Sprinkle roast with salt and pepper. In a large skillet, brown roast in oil on all sides; cool slightly. With a paring knife, cut about sixteen 3-in.-deep slits in sides of roast; insert one apple slice into each slit.
Place half of the remaining apples in a 4-qt. slow cooker. Place roast over apples. Drizzle with honey; top with onion and remaining apples. Sprinkle with cinnamon.
Cover and cook on low for 6-8 hours or until meat is tender. Remove pork and apple mixture; keep warm.
Transfer cooking juices to a small saucepan. Bring to a boil; cook until liquid is reduced by half. Serve with pork and apple mixture. Sprinkle with parsley if desired.