In a large bowl, combine spinach, chicken, cheddar cheese, onion, cornstarch, salt, pepper, soy sauce, soup, sour cream, mushrooms, and mayo. Put a layer of noodles in the bottom of a greased 9x13x2 inch lasagna pan. Spread half of the spinach mixture over noodles. Place another layer of the noodles on top and cover with the remaining spinach mixture. Sprinkle parmesan cheese then pecans on top and bake for 1 hour.