Preheat oven to 425°F. Spray an extra-large, rimmed baking sheet (20x15), or 2 large ones (18x12), with non-stick cooking spray.
Place sweet potatoes, carrots, parsnips, acorn squash, and red onion in a large bowl. Add olive oil, vinegar, syrup, and thyme. Season generously with salt and black pepper. Toss to coat.
Spread vegetables on prepared pan(s) in a single layer. Roast uncovered 40-45 minutes until vegetables are softened and browned, stirring halfway through.
Can be made 3 hours ahead. Transfer to clean baking sheet and let stand at room temperature. Rewarm at 375°F for 10-15 minutes. Serve with Carrot Top Cashew Pesto as desired.
