Preheat the oven to 400°F. Whisk 6 tablespoons of the melted butter with the oil, Sriracha, salt, pepper, and cinnamon in a large bowl. Add the squash and toss to coat. Dump the squash onto two rimmed baking sheets in a single layer.

Roast for 20 minutes without moving, then remove from the oven and stir, scraping the bottom to carefully flip the squash if possible. 

Sprinkle the brown sugar and chili flakes evenly over the trays, drizzle with the remaining 2 tablespoons butter, reduce the heat to 350°F and return the squash to the oven. Roast until tender and the sugar is golden and caramelized, another 15-20 minutes. Season with more salt and pepper to taste.