Place chicken in slow cooker sprayed with cooking spray; top with green peppers.
Mix all remaining ingredients except barbecue sauce and tortillas until blended; pour over ingredients in slow cooker. Cover with lid.
Cook on LOW 6 to 8 hours (or on HIGH 3 to 4 hours).
Remove chicken from slow cooker; place on cutting board. Cool 10 min.; pull into shreds with 2 forks. Return to slow cooker. Stir in barbecue sauce; cook, covered, on HIGH 15 min. Meanwhile, warm tortillas as directed on package.