1. Cut chicken into 1/2-inch-wide strips. Place chicken in a small bowl; sprinkle with fajita seasoning, tossing to coat. Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add chicken and onion; stir-fry 3 minutes. Add bell pepper; stir-fry 5 minutes or until chicken is done.
2. Place 1 tortilla on each of 4 plates. Top each evenly with chicken mixture and salsa. Top with avocado and cilantro, if desired. Fold tortillas over filling, and top with sour cream, if desired. Serve immediately.
Serve with: Chili-Dusted Mango