Combine the dry-rub ingredients. Cut the excess fat from the pork then butterfly it by cutting almost in half and opening out. Press down firmly with the heel of your hand to give an even thickness of the meat.
Put the pork and the dry rub mixture into a plastic food bag. Close the bag and give it a good shake to coat the meat then place in the fridge for at least 4, and up to 24 hours. Remove the pork from the fridge about 1 hour before cooking and allow it to come to room temperature. Then place in a saucepan and cover with 300ml orange juice and 300ml water. Cover and simmer for 2 hours then leave to cool in the liquid.
Prepare the tequila mixture by combing tequila, 5tbsp of the cooking liquid, treacle, chillies, garlic and chilli sauce. Drain the meat and place on a hot griddle pan. Pour over some of the tequila mixture to glaze and lightly char the pork. Turn the pork and repeat on all sides, basting and turning. Shred the pork using 2 forks.
Put the pork on a platter with the cheese, tomatoes, onion, avocados, tortillas and invite everyone to build their own burritos.