Preheat your oven to 375°F (190°C).

In a large pot, bring salted water to a boil and cook the jumbo pasta shells until al dente, about 9-11 minutes. Drain and rinse under cold water.

In a mixing bowl, combine the pumpkin puree, ricotta cheese, half of the shredded mozzarella, grated Parmesan, garlic powder, dried sage, ground nutmeg, and the egg. Mix until creamy.

Spread a layer of marinara sauce across the bottom of a 9x13-inch baking dish.

Stuff each cooked pasta shell with the pumpkin-ricotta mixture and place them opening side up in the baking dish.

Pour remaining marinara sauce over the top, ensuring every shell is coated, and sprinkle the rest of the shredded mozzarella.

Cover with aluminum foil and bake for about 25 minutes. Remove foil and bake for an additional 10 minutes until the cheese is bubbly and golden.

Allow to rest for 5 minutes before serving. Garnish with fresh herbs if desired.