Add the Italian dressing, ranch, chili powder, cumin, garlic, bell pepper and green chiles to a slow cooker. Whisk to combine.
Add the chicken breasts and cook on low about 3 hours or until the chicken is cooked through and tender.
With 2 forks, shred the chicken in the slow cooker. Stir the chicken and cover.
Turn the slow cooker to warm and leave for 30 minutes or until ready to serve.