Place the chunks of roast in a plastic bowl, sprinkle 2 tsp salt over beef, then pour the vinegar into the bowl. Stir the meat to get everything mixed together and cover. Chill in the refridgerator for no more than 2 hours but at least 20 minutes.
In a small sauce pan, add chiles, cover with water and boil for 15 minutes or until soft.
In a saute pan, heat the oil on medium high. Add the onions, garlic cloves, bay leaves, avocado leaves, and oregano. Sprinkle the remaining salt over the onions. Saute the onion and spice mixture for 5 minutes or until the onions are soft.
Once the chiles are soft, add them into a blender along with the onion and spice mixture and the beef bouillon cube. Add enough water to cover. Blend on high for 10 minutes.
Pour the blended chile into a large stock pot or crockpot (preferred). Take the beef out of the vinager and add the meat to the chile. Discard the vinegar. Stir the meat and chile together. Cook on the stove on medium low for 4 hours or in a crock pot all day on high.
Serve the barbacoa with fresh tortillas and white rice.