Mix Rotel, chicken broth & taco seasoning together, then pour over chicken. Cook on low for 8 hours.
Shred chicken, then mix with the remaining Rotel/broth mixture from slow cooker.
Drain and rinse black beans. Warm the beans, if desired. Mash them with a fork, leaving mixture chunky.
Scoop out contents of avocados and mash, leaving mixture chunky.
Mix mashed beans & mashed avocado together. Spread mixture evenly on warm tortillas (warm tortillas in pan on stove over med-low heat). Sprinkle with cheese. Add a scoop of chicken mixture and a dollop of sour cream.