Preheat your oven to 350 degrees F. Lightly spray a 9 x 13 inch baking dish with cooking spray.

Pour about half of the marinara sauce into the bottom of the dish and spread it evenly.

Cook the jumbo shells in a large pot of boiling water according to the package directions, but aim for "al dente" (usually 1 to 2 minutes less than the box suggests). Drain and rinse with cold water to prevent sticking.

In a large bowl, combine the squeezed dry spinach, ricotta, 1 1/2 cups of the mozzarella, Parmesan, egg, basil, salt, and garlic powder. Stir with a fork until well combined. Add a pinch of nutmeg if desired.

Stuff each cooked shell with approximately 2 tablespoons of the cheese and spinach mixture.

Arrange the shells in the prepared baking dish, open side up.

Pour the remaining marinara sauce over the tops of the shells and sprinkle with the remaining 1/2 cup of mozzarella cheese.

Cover the dish with foil and bake for 25 to 30 minutes.

Remove the foil during the last 5 to 10 minutes of baking to allow the cheese to become bubbly and slightly golden.

Serve warm and enjoy!