Preheat the oven. Preheat the oven to 425°F (220°C). Line a large rimmed baking sheet with parchment paper to help prevent sticking and make cleanup easier.
Prepare the squash. Wash and dry the delicata squash thoroughly. Trim off both ends, slice each squash lengthwise, and scoop out the seeds with a spoon. Cut the squash into half-moon slices about 1/2 inch thick. There is no need to peel delicata squash because its thin skin becomes tender during roasting.
Season the slices. Place the squash slices in a large mixing bowl. Add the olive oil, maple syrup, chopped sage, salt, black pepper, and cinnamon, if using. Toss until the slices are evenly coated.
Arrange on the baking sheet. Spread the squash in a single layer on the prepared baking sheet, leaving a little space between the pieces. Avoid overcrowding the pan so the squash roasts rather than steams.
Roast until tender. Bake for 20 to 25 minutes, flipping the slices halfway through cooking. The squash should be fork-tender, with caramelized edges and lightly browned surfaces. If needed, roast for a few additional minutes until the edges develop more color.
Finish and serve. Remove the squash from the oven and taste for seasoning. Add a few fresh sage leaves for garnish, if desired, and serve warm.