Preheat your oven to 200°C (390°F). Arrange the pumpkin chunks on a baking sheet lined with parchment paper, toss with 1 tablespoon of olive oil, a pinch of nutmeg, and a pinch of salt. Roast for 30-35 minutes until edges are caramelized and flesh is soft, smelling sweet and smoky.
While the pumpkin roasts, bring a large pot of salted water to a boil. Cook the pasta until al dente, about 10 minutes, then drain and set aside.
In a skillet, heat the remaining 2 tablespoons of olive oil over medium heat. Add the diced onion and sauté until translucent and fragrant, about 5 minutes, until it begins to soften and turn slightly golden.
Add the minced garlic and chili flakes to the skillet, cooking for about 1 minute until fragrant, with a gentle sizzle and aroma filling the air.
Remove the roasted pumpkin from the oven and let it cool slightly. Transfer the pumpkin to a blender, adding 1 cup of vegetable broth, and blend until smooth and creamy, watching it turn into a vibrant, velvety purée.
Pour the pumpkin purée into the skillet with the sautéed onion and garlic. Warm through, stirring gently, until the sauce is heated and slightly thickened, about 2-3 minutes.
Add the cooked pasta to the skillet, tossing to coat each piece evenly in the warm, fragrant pumpkin sauce. If needed, add a splash more vegetable broth to loosen the sauce for a silky consistency.
Finish by sprinkling grated Parmesan over the pasta and giving it one last gentle toss. Drizzle with a little olive oil for sheen and richness, and serve hot, garnished with extra Parmesan if desired.