Preheat oven to 425°F. Toss squash with 2 tablespoons oil, salt, and pepper; spread on baking sheet. Roast 25-30 minutes until tender and caramelized, stirring halfway.
Keep broth gently simmering in saucepan. Heat remaining 1 tablespoon oil and 1 tablespoon butter in large heavy-bottomed pot over medium.
Cook onion about 4 minutes until softened; add garlic and cook 1 minute. Stir rice to coat; toast 2 minutes until edges turn translucent.
Add wine; stir until fully absorbed. Add warm broth one ladle at a time, stirring frequently and letting each addition absorb before adding more.
Continue about 20-25 minutes until rice is creamy and tender with slight bite. Stir in half the squash, mashing slightly to incorporate.
Remove from heat; stir in remaining 2 tablespoons butter, sage, and Parmesan. Season with salt and pepper; top with remaining squash and serve immediately.