Preheat your oven to 400°F (204°C). Line two large rimmed baking sheets with parchment paper to prevent sticking and ensure easy cleanup.
Using a sharp chef's knife, trim the top and bottom off the butternut squash. Use a Y-peeler to remove the tough outer skin until the bright orange flesh is exposed.
Slice the squash in half lengthwise and use a metal spoon to scrape out the seeds and stringy pulp. Cut the squash into uniform 1-inch cubes to ensure even cooking.
In a large mixing bowl, whisk together the olive oil, maple syrup, chopped rosemary, salt, black pepper, garlic powder, and cinnamon.
Add the squash cubes to the bowl and toss thoroughly until every piece is well-coated with the oil and spice mixture.
Divide the squash between the two prepared baking sheets. Spread the cubes into a single layer, ensuring they are not crowding each other; this allows the air to circulate so they roast rather than steam.
Roast for 30 to 40 minutes, using a spatula to toss the cubes halfway through the cooking time.
The squash is done when it is fork-tender and the edges have developed a deep, caramelized golden-brown color.
Remove from the oven and serve immediately as a savory-sweet side dish.