In a large bowl, mix ricotta, spinach, 1 cup mozzarella cheese, ¼ cup Parmesan cheese, egg, parsley and seasonings.
In a separate large bowl, mix spaghetti sauce and water; spread 1 cup of spaghetti sauce miture into a 13x9 inch baking dish sprayed with non-stick cooking spray.
Fill uncooked manicotti shells with ricotta mixture; arrange in a single layer over sauce. Pour remaining spaghetti sauce mixture over top. Sprinkle with remaining mozzarella cheese and Parmesan cheese.
Bake, uncovered, for 40-50 minutes or until manicotti is tender.
Freeze option: Cover and freeze unbaked casserole. To use, partially thaw in refrigerator overnight. Remove from refrigerator 30 minutes before baking. Preheat oven to 350 degrees. Bake casserole as directed, increasing time as necessary to heat through and for a thermometer inserted in center to read 165 degrees.
Recipe by Tone and Tighten at https://tone-and-tighten.com/easy-spinach-manicotti.html