Preheat oven to 400°F (200°C). Line a baking sheet with parchment for easy cleanup.
Place cubed squash on the baking sheet. Toss with olive oil, salt, pepper, and cinnamon if using. Spread into a single layer.
Roast squash for 25–30 minutes, flipping halfway through, until tender and caramelized at the edges.
While the squash roasts, heat a small skillet over medium heat. Add walnuts and oil or butter. Toast for 3–5 minutes, stirring frequently, until fragrant and lightly golden. Sprinkle with a pinch of salt and remove from heat.
Transfer roasted squash to a serving dish and sprinkle with toasted walnuts. Add a light drizzle of maple syrup or balsamic glaze if desired, and finish with fresh herbs.