Sprinkle chicken with seasoning. Heat oil in a large nonstick skillet coated with cooking spray over medium-high heat. Add chicken and onion; sauté 7 to 8 minutes or until chicken is done. Remove chicken and onion from pan; wipe pan dry with paper towels.
Coat pan with cooking spray; place over medium-high heat until hot. Place 2 tortillas in pan. Sprinkle 1/4 of chicken mixture and cheese over 1 side of each tortilla. Fold tortillas in half. Cook 3 minutes on each side or until golden. Repeat procedure with remaining tortillas, chicken mixture, and cheese. Cut each folded tortilla into 2 wedges. Serve with salsa.