Combine spinach, ricotta, parmesan, mozzarella (1/2 cup), egg and Italian seasoning.
In a separate bowl, combine sauce, tomatoes and mushrooms.
Place 1 cup sauce in bottom of sprayed 13x9 baking dish.
Add a layer of uncooked lasagna noodles, half of the cheese mix, a third of the remaining sauce,a layer of uncooked lasagna noodles, half of the cheese mix, a third of the remaining sauce, a layer of noodles and remaining sauce on top. Be sure that all noodles are covered.
Cover with foil and refrigerate overnight to absorb liquids.
Bake at 350 degrees for 1 1/2 hours. (Can remove from refrigerate ahead to warm up a little before baking.)
After it's been baking for an hour, remove foil and top with mozzarella for baking during the last half hour.