Preheat the oven to 375 F.
Cut the acorn squash into half. Take out the seeds using a large spoon.
Bake in the oven for about 30 to 40 minutes. Use a fork to determine if it is ready (it should be tender).
Let the squash cool and then puree it in the blender.
Put some water to boil for the pasta.
Sautee the onions in a large pan, over medium heat. Cook for about 5 minutes, until tender.
Add the garlic and sage. Stir well. Add the milk and bring to a boil.
Add in the arugula and cook until wilted.
Cook the pasta according to package instructions. The desired texture should be al dente.
In a large bowl, mix the vegetable stock, pureed squash and salt. Add to the onion mix.
Remove from heat when the mixture begins to bubble.
Add the pasta to the pan and mix.
Transfer all the ingredients to a shallow casserole dish. Sprinkle parmesan cheese and walnuts on top.
Bake for 20 minutes. Serve hot.
