Preheat your oven to 350°F (175°C) and bring a large pot of salted water to boil.
Cook the jumbo shells according to package directions, but reduce cooking time by 1 minute to keep them slightly firm. Drain and set aside to cool.
While the pasta cooks, squeeze all excess moisture from the thawed spinach.
In a large mixing bowl, combine ricotta, drained spinach, 1 cup mozzarella, Parmesan, eggs, garlic, basil, oregano, salt, and pepper. Mix until well combined.
Spread 1 cup of marinara sauce in the bottom of a 9x13 inch baking dish.
Fill each shell with the ricotta-spinach mixture.
Arrange the stuffed shells in the prepared baking dish.
Pour the remaining marinara sauce over the shells and sprinkle with remaining mozzarella cheese.
Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 10-15 minutes until cheese is bubbly and lightly golden.