For the barbacoa: In a large crockpot, add beef brisket, beef broth, red onion, garlic, cilantro, lime juice, apple cider vinegar, chipotle in adobo and bay leaf. Cook on low heat for approximately 8 hours or until the beef can easily pull apart and salt to taste.
Wrap tortillas in a damp paper towel and microwave until flexible, approximately 15 seconds.
Evenly distribute the barbacoa and mozzarella cheese on the tortillas until there are no remaining ingredients.
Tightly roll the tortillas to form into a taquito shape.
In a large pan, warm vegetable oil for frying. Using tongs, carefully work in batches to place the taquitos face down in the oil. The oil is the right temperature if it slightly sizzles when the taquitos are submerged. Fry the taquitos approximately 3-5 minutes on each side.
Remove the taquitos from oil and place on a paper towel lined plate. Allow to sit for a couple of minutes, to allow the excess oil to absorb into the paper towel.
In a blender, add cream cheese, milk, avocado and cilantro. Blend until smooth to form the creamy avocado dipping sauce. Transfer the sauce to a small bowl.
Transfer the taquitos to a large plate and serve with the creamy avocado dipping sauce.