Heat a pot over medium heat and sauté the diced onions and minced garlic until fragrant.
Add the ancho chiles, guajillo peppers, tomatoes, beef bone broth, enchilada sauce, and all spices. Bring to a light boil.
Place the lean steak in a slow cooker and pour the blended birria sauce over the meat.
Cook on low for 6 to 8 hours or high for 4 to 5 hours until the beef becomes tender.
Remove the beef and shred it using two forks.
Lay out tortillas and fill each with rice, shredded birria beef, mozzarella cheese, onions, and cilantro.
Wrap the burritos tightly.
Enjoy immediately or wrap and freeze for later.
