Preheat oven to 450 °F. Bring a medium saucepan of water to a boil. Add onions and boil for 1 minute. Drain and rinse under cold running water. Using a sharp paring knife, trim root ends and peel.
Combine the onions, carrots, turnips, oil, 1 teaspoon maple syrup, salt, pepper and thyme sprigs in a large bowl; toss to coat well. Spread the vegetable mixture in a single layer on a large baking sheet with sides. Roast, turning the vegetables twice, until tender and lightly browned in spots, about 30 minutes.
Transfer the vegetables to a large bowl; remove thyme stems. Drizzle with the remaining 1 teaspoon syrup, vinegar and 1 tablespoon parsley; toss to coat. Sprinkle with the remaining 1 tablespoon parsley and serve.
120 calories;4 g fat(1 g sat); 5 g fiber; 21 g carbohydrates; 2 g protein; 50 mcg folate; 0 mg cholesterol; 12 g sugars; 2 g added sugars; 11930 IU vitamin A; 28 mg vitamin C; 77 mg calcium; 1 mg iron; 418 mg sodium; 477 mg potassium