Remove from packaging and place tenderloin inside slow cooker.
Brush on 1-2 tablespoons of BBQ sauce over top of tenderloin.
Cook in slow cooker for 4 hours on high setting or until shreds easily.
Shred the cooked pork using two forks pulling the meat apart.
Pour the BBQ sauce over the shredded meat and mix together until coated.
Continue to cook on low setting for 1-2 hours.
In the meantime, slice onions into rings and place in frying pan with olive oil to saute. Simmer on low for 1 hour.
When ready, assemble all ingredients for making pulled pork sandwiches.