Place the chicken breasts or thighs in the bottom of the slow cooker.
Sprinkle chili powder, cumin, smoked paprika, oregano, salt, and black pepper evenly over the chicken.
Add the minced garlic.
Pour the salsa and chicken broth over the chicken.
Add the fresh lime juice.
Cover the slow cooker with the lid.
Cook on LOW for 5–6 hours or HIGH for 2½–3½ hours, until the chicken is fully cooked and tender.
Transfer the cooked chicken to a large bowl.
Shred the chicken using two forks.
Return the shredded chicken to the slow cooker.
Stir the chicken into the cooking juices.
Let it sit for 5–10 minutes so it absorbs the flavorful liquid.
Warm the tortillas in a dry skillet for about 20–30 seconds per side.
Fill each tortilla with shredded chicken.
Add lettuce, tomatoes, avocado, cheese, red onion, and cilantro.
Finish with fresh lime juice and your favorite salsa.
Serve immediately.