Mix mayonnaise, sour cream and Seasoning in large bowl until well blended. Add chicken, celery, onion and 1/4 cup of the Salad Toppins; toss to coat well. Cover.
Refrigerate at least 30 minutes or until ready to serve.
Divide salad greens and tomato evenly among 4 serving plates. Top each with chicken salad. Sprinkle with remaining 2 tablespoons Salad Toppins.