Preheat your oven to 375°F (190°C).
Cook the pasta shells according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine ricotta, Parmesan, spinach, garlic, salt, pepper, and nutmeg. Mix well.
Spread half the marinara sauce in the bottom of a baking dish.
Fill each shell with the ricotta mixture and place it in the baking dish.
Top with the remaining marinara sauce and sprinkle mozzarella cheese over the top.
Drizzle olive oil on top for added flavor.
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes, until the cheese is golden and bubbly.
Let cool slightly before serving.