Set the oven rack in the center position in oven and preheat to 375°F. Line the baking sheet with foil. Place squash, onions, garlic, rosemary, salt and pepper on the sheet and drizzle with the olive oil. Toss to coat.
Place on center rack in the oven. Roast until tender and brown around edges, stirring every 10 min., about 30 min.
Toss in shallow bowl with Parmesan cheese. Serve and enjoy!