Clean and cut the potatoes in half. Peel the parsnips and chop them into pieces. Clean and chop the onion.
Put the chopped up veggies into a large bowl and pour the oil over them and toss. Add the herbs and seasonings and toss again to make sure all the veggies are covered with the herbs.
Spray the oven liner with oil.
Grill for about 10 minutes on medium, but check them around the 5 minute mark to make sure they aren't burning, if they are turn the heat down a bit; then flip and grill the veggies 5 more minutes. Test with a fork to make sure the veggies are tender.