Heat the oil in a pot. Add the pork shoulder, then pour in the steak sauce, apple cider vinegar and chicken broth. Stir in the brown sugar, mustard, Worcestershire sauce, ground chilli, onion, garlic and thyme. Cook for 5-6 hours (110°C), until the pork is tender. Remove the pork and shred the meat using two forks. Place the shredded pork back in the pot and mix with the juices. Spread the burger buns with butter and toast in a pan until golden. Spread on Vilnius Originalus mayonnaise, use a spoon to add the pork, then place the red onion on top.