Preheat the oven to 200°C (390°F).
To prepare the butternut squash, give it a quick rinse and cut in half, leaving the skin on. Remove the tough parts of the stem and bottom end, scoop out the seeds with a spoon, and cut each half into 1-inch slices. (You can roast the seeds as a garnish or snack).
Drizzle the olive oil over a large oven dish, then add the sliced butternut squash, onion, and whole garlic cloves. Spread the veg evenly, sprinkle with salt and pepper, and roast in the oven for 25 minutes or until the veg is tender and lightly browned. Note: Make sure this is a large dish with high sides as it's what you'll use for the pasta bake.
To a blender, add the mixed nuts/seeds, 2 tablespoons of the nutritional yeast, ½ teaspoon of the dried sage, and a pinch of salt and pepper. Pulse a few times until you have a fine crumbly mixture, being careful not to overdo it. Remove and set aside.
Bring a large pan of salted water to the boil. Add the dried pasta and kale and cook for just over half the time specified on the pasta cooking instructions, which should be around 6-7 minutes (the pasta will continue to cook in the oven). After 6-7 minutes, drain the pasta and kale and set aside.
Once the veg has roasted, remove it from the oven but leave the oven on. Transfer all the roasted ingredients to the blender and add 2 tablespoons of nutritional yeast, 1½ teaspoons of dried sage, the plant-based milk or stock, Dijon mustard, lemon juice, salt, and pepper. Blend until smooth. If you don't have a large blender, you may need to do this in batches as you don't want to overfill a blender with hot ingredients.
In the same large oven dish, add the drained pasta, kale, and blended butternut squash mix. Combine everything well in the oven dish, then sprinkle over the blended nut/seed mix. Place in the oven and bake for around 25 minutes or until the pasta is cooked through and the top of the bake has started to turn golden-brown. Serve warm.