Position racks in the upper and lower thirds of your oven and preheat the oven to 400 degrees F. Generously coat two baking sheets with nonstick spray.
Place the squash cubes in a large bowl. Drizzle with the olive oil and maple syrup, then sprinkle the salt, cinnamon, and pepper over the top. Toss to coat, then divide between the two baking sheets, discarding any excess liquid with that collects at the bottom of the bowl. Spread the cubes in a single layer on the prepared baking sheets, taking care that they do not overlap.
Place the pans in the upper and lower thirds of your oven and bake for 15 minutes. Remove the pans from the oven, turn the cubes with a spatula, then return to the oven, switching the pans’ positions on the upper and lower racks. Continue baking until the squash is tender, about 10 to 15 additional minutes. Remove from the oven and sprinkle the rosemary over the top. Serve warm.
TO MAKE AHEAD: Squash can be diced 1 day in advance. Store cubes in an airtight container in the refrigerator until ready to bake.
TO STORE: Store leftovers in an airtight storage container in the refrigerator for 4 to 5 days.
TO REHEAT: Reheat gently over low heat in a skillet on the stovetop, in the oven at 350 degrees F, or in the microwave until warmed through. Between these three options, the oven or skillet will give you the best consistency.
TO FREEZE: Lay cooked butternut in a single layer on baking sheets, and place in the freezer until frozen. Place frozen squash in an airtight freezer-safe storage container in the freezer for up to 3 months. Let thaw in the refrigerator the night before reheating. Note that when frozen, roasted vegetables will become somewhat more mushy (but they are certainly safe to eat and we don't mind a little mush for the convenience!).