Preheat the oven to 375°F. Peel parsnips and cut in half lengthwise, leaving out the core if it is tough. Cut stips into 4-inch lengths. Cut the Scallion bunches into 6-inch lengths, then steam them for 5 minutes.

In a large bowl, toss the carrots and parsnips with the oil. Transfer the vegetables to a shallow roasting pan large enough to hold the vegetables in a single layer, leaving any excess oil in the bowl. Arrange the vegetables in one layer. Season them with pepper. Roast, turning once or twice, for 30 minutes.

After 30 minutes, toss the green onions in the remaining oil and add to the roasting pan. Roast until all the vegetables are well browned, 15 to 20 minutes longer. Season with salt. Serve very hot, garnished with the parsley.