Bring a medium saucepan of water to a boil. Remove from heat and soak the dried ancho peppers for 15 minutes. Cut the stem off and shake the seeds out.
Cube the sirloin. Place the cubed sirloin and beef shank in a large covered dish. Season with salt and pepper.
Add the reconstituted ancho peppers, chipotle peppers in adobo, whole peeled tomatoes, apple cider vinegar, garlic cloves, oregano, cumin and smoked paprika to a food processor. Blend until smooth.
Add the marinade to the dish with the meat and toss to coat. Marinate overnight or at least 4 hours.
To prepare the meat, transfer the meat with marinade to a slow cooker. Add the cinnamon stick, bay leaves and chicken stock. Set the slow cooker to LOW and cook for about 4 hours until the meat is tender. Shred the meat. Remove the bay leaves and cinnamon stick from the stew.
Dip the tortillas in the stew. Top with shredded meat, onions from the stew and shredded cheese. Fold in half and fry over medium heat until tortillas are crispy and the cheese is melted.
Serve immediately with cilantro, avocado and stew for dipping.