Place the chicken breasts in the bottom of the slow cooker. Season with chili powder, cumin, garlic powder, smoked paprika, and salt.
Add the fire-roasted diced tomatoes with their juices, diced green chiles, black beans, and frozen corn over and around the chicken.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours, until the chicken is completely cooked through and shreds easily.
Remove the chicken from the slow cooker and shred it with two forks. Return the shredded chicken to the pot and stir to combine with the beans, corn, and tomatoes.
Squeeze the lime juice into the mixture and stir well. Let everything sit together for 5 minutes to let the flavors meld.
Warm the tortillas in a dry skillet or wrapped in damp paper towels in the microwave for about 30 seconds.
Spoon the chicken taco filling into the warmed tortillas and top with avocado, sour cream, fresh cilantro, and shredded cheese. Serve immediately.