Preheat your oven to 400°F (200°C). Toss the peeled and cubed butternut squash with 1 tablespoon of olive oil, salt, pepper, and half of the dried sage. Spread the cubes on a baking sheet in a single layer. Roast for about 25-30 minutes or until tender and lightly caramelized, turning halfway through for even cooking.
While the squash roasts, bring a large pot of salted water to a boil. Add your pasta and cook according to package instructions until al dente. Drain and set aside, reserving about 1/2 cup of pasta water in case you want to loosen the sauce later.
Heat the remaining tablespoon of olive oil in a skillet over medium heat. Add the chopped onion and cook until translucent, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant. Add the fresh spinach and sauté until wilted. Season with salt, pepper, and the remaining sage.
In a large mixing bowl, combine the cooked pasta, roasted butternut squash, sautéed onion, garlic, and spinach mixture. Add the ricotta cheese and half of the mozzarella and Parmesan cheeses. Gently toss everything together, adding reserved pasta water if you want a looser mix.
Transfer the mixture into your baking dish. Sprinkle the remaining mozzarella and Parmesan evenly over the top. Bake uncovered at 375°F (190°C) for 20-25 minutes, or until the cheese is melted and golden brown on top.
Let the pasta bake rest for 5 minutes before serving. This allows the flavors to meld and makes it easier to slice. Enjoy your comforting, cheesy, and flavorful Butternut Squash Sage Pasta Bake!