Place the onions, garlic, and broth in a slow cooker.
In a small bowl, combine the sugar, chili powder, salt, cumin, cinnamon, and oregano and mix well.
If you are making your own barbecue sauce using recipe above, prepare it now.
Pat the pork with a paper towel and rub the prepared mixture all over it. Place pork on top of broth in slow cooker.
In the same small bowl, mix the barbecue sauce and the soy sauce. Stir to combine. Pour on top of pork making sure the mixture is spread evenly on top. Cover and cook on low for 8 hours.
Remove pork from slow cooker and allow to cool slightly. If using bone-in pork, discard bone. Place pork in 9" × 13" casserole dish.
Shred the pork using a fork. Add additional barbecue sauce and slow cooker mixture if you’d like. Serve immediately.