Preheat oven to 375 degrees F.

Give the baking dish a quick spray with some non-stick cooking spray and then pour in some sauce and spread to make a thin layer covering the whole bottom of the dish, about 1/8 inch.

Add a layer of uncooked lasagna pasta

Now cover the pasta with a thin layer of sauce, then ricotta cheese on top of that. Then spread out a layer of thawed cooked spinach. On top of that, add a thin layer of sauce.

Add another layer of noodles, sauce, ricotta cheese, spinach, sauce. There will always be sauce touching both sides of the lasagna noodles.

Add final layer of lasagna noodles (the 3rd) and cover well with remaining sauce. Now add a nice layer of shredded mozzarella cheese and cover the whole dish with aluminum foil.

Bake for 45 minutes, remove aluminum foil, and continue baking for another 10-15 minutes.