Rub the adobo seasoning on the meat. Let marinate in the refrigerator overnight

Put meat in slow cooker. Top with onions and barbecue sauce

Cook on low for 8 to 10 hours or high for 4 to 5 hours

Remove the meat from slow cooker. Cut off and discard any excess fat and bone if necessary

Shred the meat using two forks

Return the meat to slow cooker stir until evenly coated with the sauce

Add additional barbecue sauce to the bun before assembling the sandwich if desired