Place the chicken breasts at the bottom of the slow cooker.
In a large mixing bowl, combine the black beans, uncooked rice, diced tomatoes (with their juices), chicken broth, chili powder, cumin, garlic powder, onion powder, salt, and pepper. Stir well until everything is evenly mixed.
Pour the mixture over the chicken in the slow cooker, ensuring the chicken is covered.
Cover the slow cooker and set it to low heat for about 6 hours (or high heat for about 3 hours).
Once cooking time is complete, use two forks to shred the chicken in the slow cooker. Stir everything together to combine.
Taste the mixture and adjust seasoning if necessary.
Serve in large flour tortillas, topped with shredded cheese and your choice of optional toppings like sour cream, salsa, chopped cilantro, avocado, and lime wedges.