Place the chicken breasts in a slow cooker. In a small bowl, mix together chili powder, cumin, garlic powder, onion powder, salt, and black pepper. Rub the spice mixture over the chicken.

Cover and cook on low for 6-8 hours or on high for 3-4 hours until the chicken is cooked through and easily shreds with a fork.

Once cooked, remove the chicken from the slow cooker and shred it using two forks. Return the shredded chicken to the slow cooker and mix it with the juices.

Warm the corn tortillas in a skillet over medium heat until pliable. Fill each tortilla with shredded chicken, lettuce, tomatoes, cheese, sour cream, and cilantro.

Serve immediately and enjoy your delicious shredded chicken tacos!