Cook chicken in cooking spray until browned. I actually used Extra Virgin Olive Oil instead of the cooking spray and I also sprinkled garlic and onion powder on it first to let it have a little more flavor. In a bowl, combine the ranch dressing, the mayo and the fajita seasoning mix.
Add chicken, celery, peppers and green onion. Toss well to coat. Cover and refrigerate for 1 – 2 hours. Spread generous 1/2 cup of chicken mixture over toasted tortilla. Top with additional toppings as desired.