Spray slow cooker lightly with cooking spray. Put sliced onions on the bottom. Rinse pork loin and pat lightly with paper towels. Coat pork with a layer of Lawry's Seasoning Salt and some pepper. Place on top of onions.
In a medium sized bowl, mix 1/2 bottle of barbecue sauce and a can of diet soda. Pour the fizzy concoction on top of seasoned pork loin in crock pot.
Cover the crock pot and cook on LOW for about 7-8 hours, or until meat is fork tender. When the meat is tender enough, carefully take the pork out of the slow cooker and place on a plate and shred the meat up using two forks. Place meat back inside crock pot, stirring to combine, and let cook for another 30 minutes.
Serve on buns and ENJOY!!