1In medium bowl, mix chili powder, cumin, salt, garlic and lime juice. Add chicken, bell pepper and onion; stir to coat. Cover bowl; refrigerate at least 2 hours to marinate, turning once.
2Heat gas or charcoal grill. Cut 2 (18x12-inch) sheets of heavy-duty foil. Remove chicken and vegetables from marinade; discard marinade. Place half of chicken and vegetables on center of each sheet. Bring up 2 sides of foil so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion. Fold other sides to seal. Cut another sheet of foil; wrap tortillas securely in foil.
3Place packets on grill over medium heat. Cook chicken and vegetables 10 to 15 minutes or until chicken is no longer pink in center and vegetables are crisp-tender. Cook tortillas 2 to 3 minutes or until warm. Open foil carefully to allow hot steam to escape.
4Serve each chicken and vegetable packet with 2 tortillas. If desired, top tortillas with shredded lettuce, sour cream, guacamole, shredded cheese and salsa.