Preheat the oven to 375°F (190°C).

Cook the pasta shells according to the package instructions until al dente, then drain and set aside.

In a mixing bowl, combine pumpkin puree, cashew cheese, nutritional yeast, garlic powder, onion powder, salt, and pepper. Mix until smooth.

Spread a thin layer of marinara sauce at the bottom of a baking dish.

Stuff each pasta shell with the pumpkin mixture and place them in the baking dish.

Pour the remaining marinara sauce over the stuffed shells.

Cover the dish with foil and bake for 20 minutes.

Remove the foil and bake for an additional 10 minutes until heated through.

Garnish with fresh basil if desired and serve.