Toss squash with 4 teaspoons oil, salt and ¼ teaspoon pepper. Spread evenly on a large baking sheet. Roast, stirring occasionally, until tender throughout and lightly browned, 30 to 45 minutes (depending on the variety of squash).
Heat the remaining 2 teaspoons oil in a small skillet over medium heat. Add garlic and cook, stirring, until fragrant but not brown, 30 seconds to 1 minute. Toss the roasted squash with the garlic and parsley. Taste, adjust the seasoning and serve.
Consider cutting squash up to 1 day ahead; store airtight in the refrigerator.