01 - Set the oven to 375°F (190°C) to prepare for roasting.
02 - Peel and cut carrots, parsnips, and turnips into uniform 1.25-inch pieces; halve the onion.
03 - In a large bowl, combine all vegetables with olive oil, salt, pepper, and dried thyme until evenly coated.
04 - Spread the vegetables in a single layer on a baking sheet to ensure even cooking.
05 - Place the tray in the oven and roast the vegetables for 35 to 40 minutes, turning halfway through to achieve uniform browning.
06 - Remove from oven and serve immediately as a warm, low-fat side dish.