1) Cook pasta according to package. Drain and rinse with cool water.
2) Whisk together mayonnaise, sour cream, Olive Garden Italian dressing, garlic, salt, pepper and lemon juice in a large bowl. Add green onions and olives. Fold in pasta, chicken and Parmesan cheese. Chill.
3) Just before serving, stir in Romaine lettuce, tomatoes and croutons.