Place your pork roast and chopped onion in a large crock pot. Add beef broth and cook on low for 6 to 8 hours.
Once cooked, shred the pork with two forks. Leave the pork in the crock-pot until ready to use
Mix the re-fried beans and the taco seasoning together and spread on the bottom part of the the bun.
Next add your pork, cheese, onion, and avocado.
On the other half of the bun add your Dijon mustard. Place the bottom bun and top bun facing up on a cookie sheet. Broil them for about 2 minutes or until the cheese is melted and the buns are toasted.