Heat the oven to 400°F. Line a rimmed sheet pan with parchment paper.
In a large bowl, combine the egg, breadcrumbs, milk, grated onion, 1 tablespoon of the ketchup, Worcestershire sauce, thyme, garlic powder, salt, and black pepper. Add the ground turkey and mix gently until just combined.
Shape the mixture into a compact loaf in the center of the prepared pan. Spread the remaining tablespoon of ketchup over the top.
Place the carrots, parsnips, and sweet potato around the meatloaf. Drizzle the vegetables with olive oil and toss them on the pan to coat. Spread them in a single layer.
Roast for 35 to 45 minutes, until the vegetables are tender and the center of the meatloaf reaches 165°F. If the vegetables finish first, transfer them to a serving dish and let the meatloaf continue cooking.
Let the meatloaf rest for 5 minutes before slicing. Serve with the roasted root vegetables.