Prep. Place sliced onions and garlic in a single layer along the bottom of a slow cooker (for Instant Pot method, see note 1). Pour chicken stock on top.
Pork. In a small bowl, whisk together the erythritol, salt, chili powder, and cumin. Pat the pork roast dry with paper towels, then evenly rub the spice mix over the pork. Place in the crockpot.
Cook. Cover and cook for 6-8 hours on high, or 8-10 hours on low. Once the pork is fork-tender, remove it to a cutting board. Remove onions to the cutting board. Discard all liquid from the crockpot.
Chop. Roughly chop the onions and return them to the crockpot.
Shred. Once cool enough to handle, use 2 forks to shred the pork roast, removing any large pieces of fat. Place shredded meat back into the crockpot.
BBQ sauce. Whisk BBQ sauce ingredients together in a medium bowl. Pour over the pork and toss to thoroughly combine. Serve with extra sauce and enjoy!