Place chicken breasts in a slow cooker with chicken broth, chili powder, cumin, garlic powder, onion powder, salt, and black pepper.
Cook on low for 6-8 hours or on high for 3-4 hours until the chicken is tender.
Shred the chicken using two forks and mix it back into the cooking juices.
Warm the flour tortillas in a pan or microwave.
Assemble each burrito by adding shredded chicken, cooked rice, black beans, diced tomatoes, avocado slices, shredded cheese, sour cream, salsa, and lettuce.
Sprinkle fresh cilantro on top.
Roll up the tortillas, folding in the sides to secure the filling.
Serve warm with extra salsa or sour cream on the side.