This can also be made ahead and refrigerated.
4 10-ounce packages of frozen chopped spinach
Cook spinach according to package directions and drain well-pressing all liquids out. Saute' mushrooms in butter or oil. Combine mayo, sour cream and parmesaan cheese. Stir in artichoke hearts, spinach and mushrooms.
Pour all into a greased 9x13-inch glass dish. Slice tomatoes 1/4 to 1/2-inch thick and place on top. If Using canned tomatoes, distribute evenly. Salt and pepper to taste. Brown bread crumbs in butter and sprinkle over all. Can also substitute dried onions if desired.
Bake at 325 degrees F. for at least 30 minutes or until heated through. If made ahead and refrigerated, bake at 350 degrees F for about 50 minutes.
Leftovers are great reheated in the microwave.