Preheat your oven to 375ºF (190ºC). Gather all your ingredients.

Bring a large pot of salted water to a boil and cook the dry pasta until it's 2 minutes shy of al dente, about 8-10 minutes. Drain and set aside.

In a skillet, melt 2 tablespoons of butter. Add the chopped walnuts and 2 teaspoons of fresh sage, toasting for about 5 minutes until fragrant.

In the same skillet, add 2 tablespoons of extra-virgin olive oil. Sauté the chopped onion and sliced mushrooms for 8 minutes until softened and browned.

Stir in the tomato paste, minced garlic, and crushed red pepper flakes. Cook for 3-4 minutes until caramelized.

Add the spinach, stirring constantly until wilted. Season mixture with dried oregano, salt, and pepper.

Pour in vegetable broth, scraping up bits from the pan. Stir in pumpkin purée, Parmesan, and Fontina until smooth.

Fold the cooked pasta into the sauce, ensuring each piece is coated. Transfer to a greased 9x13-inch baking dish.

Sprinkle remaining Fontina cheese and topped with walnut-sage mixture. Cover with foil and bake for 15 minutes, then remove foil and bake uncovered for another 10 minutes.

Let the dish rest for 5 minutes before serving.