Preheat oven to 350°F. Dice celery, onions & mushrooms. Saute in vegetable oil. Mix mayo, sour cream, water chestnuts and chicken in large bowl. Add sauteed vegetables. Top with provolone and cheddar cheese.
Layer into greased baking dish.
Bake at 350 for 1 hour. After 50 minutes remove from oven. Top with croutons. Sprinkle with parmesan cheese bake for remaining 10 minutes.