Preheat the oven to 400°. In a large bowl combine squash, onion, and 1 1/2 Tbsp olive oil. Season with salt and pepper. Spread the veggies out on a large baking sheet. Take garlic and slice away the very bottom of the clove, exposing the garlic in its peel. Rub the remaining 1/2 Tbsp of olive oil into each of the cloves. Seal the garlic in aluminum foil and add to the baking sheet. Roast the veggies and garlic for 45 mins to an hour or until slightly golden.