Cut each piece of pork tenderloin in half, to easily fit in the crockpot.
Place slices from 1 onion on bottom of crockpot. Add pork. Cover pork with remaining onion slices.
Pour ½ of the bottled barbecue sauce over top. Cover and cook on high setting for 30 minutes. Turn temperature down to low and cook for about 3½ -4 hours, until it’s easy to shred with a fork.
Remove tender-cooked pork to a cutting board or large plate and shred with a fork. Discard sauce from crockpot. In a large bowl, add shredded pork and remaining barbecue sauce. Toss to coat well. Just before serving, heat shredded pork in microwave before serving.
To assemble sandwiches: Heat the buns or sandwich thins slightly in the microwave or oven. Mound ½ cup of pork on bottom of the bun or sandwich thin. Top each with ½ coleslaw and another half of bun or sandwich thin. Leftover pork freezes great.