1. Preheat oven to 425°F (220°C). Bring salted water in a large pasta pot to a boil. While the water is coming to a boil, heat olive oil in a pan. Sauté onion and garlic in olive oil with chili flakes, sage, salt, and pepper to taste until onions are translucent. Set aside.

2. Cook the pasta and squash in the same pot until tender. Measure out the pasta water, and then drain the pasta. Set the pasta and squash aside. 

3. In the pasta pot, mix the pasta water, milk, goat cheese, onion-garlic mixture, toasted walnuts (set 2 tbsp. aside for topping), bacon, and ⅓ cup of shredded cheese. Add the squash and pasta and toss together until well mixed.

4. Transfer pasta mixture to a 9 x 9-in (2 L) baking dish. Top with the reserved walnuts and remaining cheese. Season with pepper. Bake for 20 minutes, or until top is golden brown. 

Option: To garnish and add flavour, toss 4 to 5 whole small sage leaves with a 1 tsp. olive oil. Place on top of pasta before baking.