Preheat the oven to 200°C/Gas Mark 6. Lightly oil a baking tray and arrange the butternut squash cubes on it. Sprinkle with salt and pop in the oven. At the 20-minute mark, take out the tray, flip the cubes over with a spatula, sprinkle over the sage leaves, then rotate the tray. Put it back in the oven for another 10-15 minutes until the butternut squash is golden brown and tender.
While the butternut is roasting, make the sauce: Heat 1 tbsp olive oil in a small pan over medium-low heat. Add the garlic and cook, stirring for 1-2 minutes, or until fragrant but not browning. Add the almond milk and a generous pinch of salt and pepper and bring to a simmer, stirring occasionally, for 3 minutes at a simmer. Remove from the heat and transfer to a blender.
Add the cashews, nutritional yeast, lemon juice and garlic powder and blend until smooth. Season to taste.
Cook the pasta according to the packet instructions. Drain and mix in a few spoonfuls of sauce, tossing to combine. Fold in the roasted butternut and crispy sage leaves, adding more sauce for the desired consistency. Top with fresh sage leaves and toasted walnuts.