Preheat the oven to 375°F (190°C).
Cook the pasta shells according to package instructions until al dente.
Drain the shells and set them aside to cool.
In a mixing bowl, combine pumpkin purée, Gouda, ricotta, nutmeg, salt, and pepper.
Stuff each shell with the pumpkin mixture.
Spread 1 cup of marinara sauce in the bottom of a baking dish.
Arrange the stuffed shells on top of the marinara sauce.
Pour the remaining marinara sauce over the shells.
Sprinkle with Parmesan cheese.
Cover the dish with foil and bake for 20 minutes.
Remove the foil and bake for an additional 15 minutes.
Remove from the oven and let cool for a few minutes.
Serve warm, garnished with fresh basil.