Preheat the oven to 400˚F. Line a large baking sheet with parchment paper.
Cut off both ends of the squash then cut the squash in half lengthwise. Scrape out and discard the seeds. Cut the squash into ½-inch slices and transfer them to a large bowl. Add the olive oil, maple syrup and Dijon mustard, and season with salt and pepper. Toss to coat (I find it’s best to use my hands for this!).
Arrange the squash in a single layer on the baking sheet and roast for 15-20 minutes, or until lightly golden on the bottom. Carefully flip the slices over and continue to roast for 5-10 minutes, or until golden around the edges and tender. Nudge each slice gently to ensure that it doesn’t stick to the pan (you can leave them on the pan to cool, if desired).