Cook the pasta in a large pot of well-salted water according to package directions until al dente. Reserve 1 cup of pasta water before draining.
Drain the soaked cashews and place them in a high-speed blender or food processor with the pumpkin purée, nutritional yeast, lemon juice, garlic, onion powder, smoked paprika, mustard powder, and cayenne if using.
Add the plant milk to the blender and blend everything on high until completely smooth and creamy, about 2 minutes. If the sauce seems too thick, add a little reserved pasta water to thin it out.
Return the drained pasta to the pot over low heat and add the olive oil, stirring to coat the pasta evenly.
Pour the pumpkin sauce over the pasta and stir gently to combine. Continue to cook over low heat for 2-3 minutes until the sauce thickens slightly and coats the pasta beautifully.
Season with salt and pepper to taste, adding more nutritional yeast if you’d like a stronger “cheesy” flavor.
Serve immediately in warm bowls, topped with a light sprinkle of smoked paprika and fresh herbs if desired.