Slow cooked Barbacoa beef with glazed shallots, pickled veggies on a steam bun
Place all ingredients in a crockpot. Place a sheet of parchment paper over ingredients, cover with lid. Cook on high for 4 hours or low for 6-8 hours. Using two forks shred the beef and return the to juices in the pan and keep warm until ready to serve.
Add vinegar and shallots into a medium size skillet. Cook over medium heat and bring to a low simmer until shallots begin to caramelize. Remove from heat.
In a bowl add vinegar, salt and sugar. Stir to dissolve then add sliced peppers. Place in refrigerator while beef is cooking. Can be made a day in advance.
Layer beef with caramelized shallots, pickled jalapeno peppers, ripe avocado slices and mango slices inside a steamed bun or flour or corn tortillas.