1. Scatter onions and bacon evenly over bottom of slow cooker. Place pork roast on top (cut roast in half or in thirds if it won't fit in cooker in one piece). In a small bowl, whisk together barbecue sauce, brown sugar and garlic powder. Pour sauce mixture evenly over pork. Cover and cook on low until meat is tender, about 5 hours.
2. Remove roast from slow cooker and shred meat. Return shredded meat to slow cooker, stir in beans, cover and cook until heated through, about 15 minutes. Season with salt, if desired, and serve right away.