Place chicken in a 3-qt. slow cooker. Combine lime juice and chili powder; pour over chicken. Cook, covered, on low until chicken is tender, 5-6 hours. , Remove chicken. When cool enough to handle, shred meat with 2 forks; return to slow cooker. Stir in corn and salsa. Cook, covered, on low until heated through, about 30 minutes. Place filling on tortillas; if desired, serve with sour cream, pickled onions, lettuce and cheese.