Hawaiian Pulled Pork Sandwich

INGREDIENTS

• 1 medium onion, finely chopped
• 1/2 cup ketchup
• 1/3 cup cider vinegar
• 1/4 cup packed brown sugar
• 1/4 cup tomato paste
• 2 tbsp sweet paprika
• 1 tbsp red pepper flakes
• 2 tbsp Worcestershire sauce
• 1 15oz can Pineapple, discard the sauce
• 3 tsp salt
• 2 tsp black pepper
• 1 avocado, optional
• 2.5 lbs pork butt, cut into 2 inch pieces