In a large pot, bring water to a boil and add the pasta. Cook as directed on the packaging.
Add the olive oil and garlic to a large saucepan, and cook over medium heat for 3 minutes. Add the milk, onion powder, and tapioca flour. Cook for another 5 minutes, stirring often.
Add the nutritional yeast, the pumpkin purée, and Dijon mustard to the sauce. Mix well to combine everything.
Add the cooked pasta to the saucepan, and mix well to cover the pasta with the sauce.
Garnish with green onions or herbs of choice and serve warm.