Heat oven to 325°F. Heat taco shells in oven as directed on box.
Meanwhile, in medium microwavable bowl, place chicken. Sprinkle with taco seasoning mix; toss gently to coat. Microwave uncovered on High 2 to 3 minutes or until hot. Stir in 1/2 cup dressing.
Spoon warm chicken mixture into heated taco shells. Top with lettuce, tomato, cheese and onions. Drizzle with salsa and additional dressing.