Preheat the oven to 200°C (400°F). Line a baking tray with baking paper.
Place the pumpkin on the prepared tray and bake for 20 minutes or until soft and cooked through. Transfer the pumpkin to a bowl and lazily mash it with a fork to create a lumpy mash. Reduce the oven temperature to 160°C (320°F).
Cook the macaroni according to the packet instructions until just before al dente. Drain and set aside in a medium baking dish.
Heat the olive oil in a saucepan over medium heat. Sift in the flour and stir constantly for 2 minutes until you have a roux. Once the roux starts to bubble, gradually whisk in the soy milk a little at a time. When all the milk has been incorporated, stir in three- quarters of the cheese, the garlic powder, mustard and nutritional yeast and cook, stirring, for 8–10 minutes, until thickened. Remove from the heat and stir through the nutmeg, thyme, chilli and sage.
Pour the cheese sauce over the cooked pasta, add the mashed pumpkin and gently mix to combine. Season with salt and pepper, then scatter the remaining cheese and the breadcrumbs over the top.
Transfer to the oven and bake for 30 minutes or until the breadcrumbs are crisp and golden.
Allow the mac ’n’ cheese to cool for 10 minutes before serving.