Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper.
Drizzle the cut side of the squash with a little olive oil and season with salt and pepper. Place it cut-side down on the baking sheet. Place the peeled garlic on a small piece of foil, drizzle with the remaining olive oil, and wrap tightly. Add the packet to the baking sheet.
Roast for about 30 minutes, or until the squash is fork-tender and the garlic is soft.
Bring a large pot of salted water to a boil and cook the pasta according to package directions. Before draining, reserve about 1 1/2 cups of the pasta water.
Measure 1 cup of roasted squash flesh and add it to a blender along with the roasted garlic, white beans, nutritional yeast, rosemary, cinnamon, nutmeg, onion powder, salt, pepper, and 3/4 cup reserved pasta water. Blend until completely smooth and creamy, adding more pasta water as needed to reach your desired consistency.
Return the drained pasta to the pot and pour in the butternut squash sauce.
Add the spinach and vegan parmesan and stir over low heat for 2-3 minutes, until the spinach is wilted and the sauce is warmed through. Add another splash of pasta water if needed.
Divide between bowls and top with additional vegan parmesan, red pepper flakes, and black pepper, if desired.