Place the diced onion, garlic and orange juice in your slow cooker.
In a small bowl, mix all of the spices together.
Trim all excess fat from the pork shoulder, then rub the spice mixture generously around the entire pork shoulder and place in the slow cooker.
Turn your slow cooker to low and cook for 8 hours.
Once your pork is fully cooked, remove it from the slow cooker to a plate or cutting board and use two forks to shred the pork.