Peel the butternut squash, and slice it into segments. Scoop out any seeds, and slice the segments into semicircles.
Add the butternut squash segments to a large baking tray, and drizzle them with the oil. Using your hands, coat the butternut squash with the oil.
Sprinkle the butternut squash with the cumin seeds and chili flakes, and then season with salt and pepper to taste. Add the rosemary sprigs, and the garlic cloves to the baking tray.
Bake the butternut squash for 50 minutes, turning once while it is in the oven. Serve immediately, and keep any leftovers in an airtight container in the fridge.