Cook spinach according to the directions, drain, squeezing out excess liquid.Stir in water chestnuts. Set mixture aside.
Preheat oven to 350.
In a 12" skillet, arrange chicken breasts and add 1/2 cup of the sherry and the bay leaf. Bring to boil and cover and reduce heat , allowing to simmer until no longer pink, about 20 mins.Drain and set chicken aside.
In the same skillet, melt the butter and saute the mushrooms, green onions and garlic over med heat for 5 mins, until tender, set aside.
In a med bowl, stir together mayonnaise, 1/2 cup of the parmesan cheese, sour cream and remaining sherry.
To assemble, spread spinach mixture evenly in the bottom of a 13 by 9 by 2 inch baking dish. Top with chicken breasts, artichokes,and mushroom onion mixture.
Spread the mayonnaise mixture over the top and sprinkle with thr remaining parmesan cheese.