Preheat the oven to 200°C/390°F. Place the butternut squash on a large baking tray with the olive oil and a good sprinkling of salt and pepper. Place in the oven for 20-30 minutes.
Bring a pan of salted water to the boil for the pasta. Put all the pesto ingredients in a blender and pulse until mostly smooth or you've reached your desired texture. Season with salt and pepper to taste.
When the squash is nearly ready cook the pasta. Drain and return to the pan with the pesto. Mix thoroughly then add the roasted squash, reserving a little for topping. Serve in bowls topped with a final few cubes of squash and plenty of grated parmesan.