Bring a large saucepan of water to a boil and salt generously. Cook the pasta according to the box directions until al dente and drain in a colander.
In a high-powered blender, add the pumpkin, the soaked and drained cashews, nutritional yeast, mustard powder, garlic powder, onion powder, paprika, nutmeg, salt, black pepper to taste, lemon juice, and coconut milk. Blend until the sauce is completely smooth and creamy, about 1–2 minutes. Taste for seasonings and adjust accordingly, adding more salt as needed.
Return the cooked and drained pasta back to the saucepan and add the cheese sauce.
Heat over medium heat until the sauce is well combined with the pasta and warmed through. Season the mac and cheese to taste.