Bring a large pot of water to a rolling boil. Add the pasta and cook according to the package directions until al dente.
Drain the cooked pasta thoroughly and set it aside. If desired, lightly coat it with a small drizzle of olive oil to prevent the pieces from sticking together while the sauce is prepared.
Warm the 2 tablespoons of olive oil in a pan over low heat. Add the finely diced onion and minced garlic, then sauté gently until the garlic begins to develop a light golden color.
Stir the chopped sage and thyme into the onion mixture. Continue cooking over low heat for approximately 5 minutes, allowing the onion to soften and the herbs to release their aroma.
Transfer the sautéed onion, garlic, sage, and thyme to a blender or food processor. Add the pumpkin purée, almond milk, coconut cream, nutritional yeast or cashew Parmesan, nutmeg, sea salt, and black pepper.
Process the mixture until the sauce is completely smooth and evenly blended.
Add the arrowroot starch to the blended sauce. Pulse several times until the starch has been fully incorporated. The mixture may appear relatively thin at this stage, but it will become thicker as it cooks.
Pour the sauce into a large pan and place it over low heat. Cook for about 5 minutes, stirring frequently, until the mixture reaches a thick and creamy consistency.
Taste the sauce and adjust the salt, nutmeg, or black pepper as needed.
Add the cooked pasta to the pan and gently toss until every piece is evenly covered with the pumpkin sauce.
Serve immediately. Garnish with additional nutritional yeast, cashew-based Parmesan, or red pepper flakes, if desired.