Meanwhile, in a medium microwavable bowl, place chicken. Sprinkle with taco seasoning mix; toss gently to coat. Microwave uncovered on High for 2 to 3 minutes or until hot. Stir in 1/2 cup of the ranch dressing.
Spoon warm chicken mixture into heated taco shells.
Top with lettuce, tomato, cheese and green onion.
Drizzle with additional ranch dressing if desired.