ASSEMBLY:
Reduce oven heat to 350.
Place a little sauce at the bottom of a large 3 quart casserole dish. Place a layer of squash over the sauce. By the tablespoon, add ricotta cheese and smooth it with a spoon to cover squash. Add a layer of mushrooms, and then spinach. Cover with mozzarella and a parmesean. Cover with sauce and spread with a spoon. Repeat until all ingredients are used ending wih a layer of squash. Cover with sauce, mozzarella and parm. Cover with foil and bake for 45 minutes. Remove foil and bake for another 10 minutes.