Preheat oven to 375°F (190°C) and boil salted water in a large pot.

Cook jumbo pasta shells until al dente (about 8 minutes). Drain and cool slightly.

In a mixing bowl, combine ricotta, pumpkin puree, spinach, half the Parmesan, salt, pepper, nutmeg, and Italian seasoning until creamy.

Stuff each shell with the filling using a spoon or piping bag.

Spread half of the marinara sauce in a baking dish. Place stuffed shells upright and top with remaining sauce and Parmesan.

Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 5 minutes until golden.