In a large pot with boiling salted water cook mostaccioli until al dente.
Drain.
In a large bowl combine spaghetti sauce, grated Parmesan cheese, and cooked and drained pasta.
In a separate bowls place cooked spinach and shredded mozzarella cheese. Reserve 1/2 cup of shredded mozzarella cheese for top.
To assemble, in a 1 1/2 quart casserole dish layer half of the noodle mixture, spinach, and shredded mozzarella cheese. Repeat. Cover with aluminum foil.
Bake in a preheated 350 degree F(175 degree C) oven for 30 minutes.
Remove from oven, sprinkle remaining 1/2 cup shredded mozzarella cheese over top and bake until cheese melts.
