Lightly grease Crock-Pot. Place pork tenderloin in pot. 

An inch apart, cut slits into pork about half way through the tenderloin. As pictured, place an apple slice or two into each slit. 

Sprinkle cinnamon over pork and top with onions. 

Cover pot and cook pork on low for 10-12 hours. 

When ready to serve, place tenderloin on a platter and shred.