In a bowl, whisk together the minced garlic, BBQ sauce, apple cider vinegar, chicken stock, brown sugar, mustard and Worcestershire sauce.
Place the pork fillet into the base of a slow cooker (or crock pot).
Sprinkle the chopped onion over the top.
Pour the sauce over the pork fillet. Stir to coat.
Cook on HIGH for 4 hours, or LOW for 8 hours.
Use two forks to shred the pork fillet (it should come apart very easily).
Stir the pork through the sauce and allow to cook for a further 20 minutes.
Serve with burger rolls and coleslaw, in tacos or salads.