Preheat the oven to 425°F. Line a large baking sheet with parchment paper or aluminum foil.
Peel the squash using a vegetable peeler. Slice off the stem and base, then cut the squash in half lengthwise. Scoop out the seeds with a spoon.
Drizzle the squash halves with olive oil, brushing to coat evenly on all sides. Season with salt and pepper.
Place the squash cut-side down on the prepared baking sheet and roast for 15 minutes, just until slightly softened. Remove from the oven and let cool until safe to handle.
Transfer the squash to a cutting board. Position one piece between two chopsticks or skewers. Using a sharp knife, make vertical slits about ⅛ inch apart across the squash, cutting straight down until the knife meets the chopsticks (do not cut all the way through). Repeat with the second half.
Return the scored squash to the baking sheet.
In a small bowl, mix the butter and chopped sage until smooth. Spread half of the butter mixture over the tops of the squash, pressing gently into the cuts.
Roast the squash for 30 minutes.
Remove from the oven, spoon the remaining butter mixture over the tops, and brush it into the cuts. Roast for another 15-20 minutes, or until the squash is fork-tender.
While the squash is in the oven for the final 15-20 minutes, prepare the topping. Place the torn bread on a small baking sheet. Drizzle with olive oil, sprinkle with garlic powder, and toss to coat evenly. Spread into a single layer and bake (along with the squash) for 8-10 minutes, or until golden and crisp.
Let the bread cool slightly, then transfer to a food processor. Add the Parmesan cheese and pulse a few times until coarse crumbs form.
Transfer the roasted squash to a serving platter. Spoon any melted butter from the baking sheet over the top, then sprinkle generously with the garlic-Parmesan breadcrumbs.
Drizzle with maple syrup, if using. Serve warm.