Bring a large pot of salted water to a boil and cook the pasta shells according to package instructions until al dente. Drain and set aside.
In a mixing bowl, combine the ricotta cheese, mozzarella cheese, chopped spinach, parmesan cheese, beaten egg, minced garlic, dried basil, dried oregano, salt, and pepper. Mix until well combined.
Spread 1 cup of marinara sauce on the bottom of a 9x13 inch baking dish.
Carefully fill each pasta shell with the ricotta-spinach mixture and place them in the baking dish, open side up.
Pour the remaining marinara sauce over the stuffed shells, ensuring they’re well covered.
Cover the dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil, and sprinkle additional mozzarella on top if desired. Bake uncovered for an additional 10-15 minutes, until the cheese is bubbly and golden.
Allow to cool for a few minutes before serving. Garnish with fresh basil leaves.
Notes
For extra flavor, consider adding a pinch of red pepper flakes to the filling.