Preheat oven to 375°.
Cook manicotti shells for 4 minutes less than package directions, drain, and rinse with cold water. Spread them out so they don't stick together.
10 manicotti shells
Combine 1 1/2 cups mozzarella, ricotta, spinach, Parmesan cheese, oregano, salt, and pepper in a large bowl.
1 1/2 cups part-skim mozzarella cheese, 15 oz part-skim ricotta cheese, 10 oz frozen spinach, 1/4 cup Parmesan cheese, 1 1/2 tsp dried oregano, 1/4 tsp salt, 1/4 tsp black pepper
Spray a 13" X 9" baking dish with cooking spray and put enough sauce in the bottom so that it covers the surface.
1 jar pasta sauce, Cooking Spray
Carefully spoon cheese mixture into manicotti shells, place in baking dish in a single layer. Top with remaining sauce.
Cover tightly with foil and bake for 30 minutes. Remove foil, top with the remaining mozzarella cheese and bake until the cheese melts, about 5 minutes.
1/2 cup mozzarella
Let stand for 10 minutes.