Combine parsnips, carrots and onion on a large sheet pan. Add rosemary, thyme, salt and pepper. Drizzle with olive oil. Using your clean hands, toss vegetables and herbs with olive oil, until well coated with oil, herbs and spice. Spread into a single layer and bake for 10 minutes.
Using a spatula flip vegetables and place back in the oven for an additional 10-15 minutes until golden and tender.