Pat the pork shoulder dry with paper towels. This helps the rub stick better and ensures a nice flavourful crust as it cooks.
In a small bowl, mix together the brown sugar, salt, paprika, cumin, black pepper, garlic powder, onion powder, and chilli powder.
Massage the spice rub all over the pork shoulder, making sure it’s well coated.
Place the pork into the slow cooker and pour the orange juice around the sides (not directly over the top so the rub stays put). Cook on low for 6–8 hours or high for 4 hours, until the meat is tender and falling apart.
Lift the pork out of the slow cooker and place it on a board. Remove any bones or excess fat, then shred the meat using two forks. It should pull apart easily.
Discard about half of the cooking liquid, then return the shredded pork to the slow cooker. Stir gently so it soaks up all those rich, flavourful juices. Leave on warm for 30 minutes before serving.