Mix chile powder, paprika, onion, garlic, and cumin together in a small bowl.
Pat chicken dry with paper towels. Lightly coat with olive oil and season with salt and pepper. Coat all sides of chicken with seasoning mix.
Pour 1/2 of the salsa in a slow cooker and spread to cover the bottom. Place chicken on top and cover with remaining salsa.
Cook on Low for 6 to 8 hours or on High for 4 hours, until chicken is no longer pink in the center and the juices run clear. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
Shred chicken with tongs and stir thoroughly so it can absorb remaining juices in the slow cooker.