Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Arrange the frozen diced butternut squash, chopped tomatoes, and sliced onion on the baking sheet. Drizzle with olive oil and season with salt, black pepper, and dried thyme. Toss until everything is evenly coated.
Roast for approximately 25–35 minutes, stirring halfway through, until the squash is tender and the tomatoes and onions are soft and lightly caramelized.
Meanwhile, bring a large pot of water to a boil. Add the fusilli and cook according to the package directions until al dente. Reserve 1/3 cup (80 ml) pasta cooking water, then drain.
Carefully transfer the roasted vegetables to a blender. Blend until smooth and creamy, adding a little reserved pasta water if necessary. Vent the blender lid appropriately and work in batches when blending hot vegetables.
Return the cooked pasta to the pot. Add the roasted butternut squash sauce and toss over low heat for 1–2 minutes. Gradually add the remaining reserved pasta water as needed.
Divide the pasta among serving plates and garnish with freshly grated Parmesan or fresh herbs, if desired. Serve immediately.
