Preheat oven to 450°F. Line 2 large baking sheets with foil.
Peel the root vegetables and cut into ¼- to ½-inch-thick slices. Place vegetables in a large microwave-safe bowl or baking dish, along with ¼ cup water. Cover with vented plastic and microwave 5–7 min., until almost tender.
Drain the vegetables well and gently toss with the oil. Arrange in single layer on lined baking sheets. Season with salt and pepper. Roast 15 min., until golden brown.
Transfer vegetables to serving bowl and spoon pesto on top. Garnish with parsley.