1. Preheat oven to 425 degrees Fahrenheit.
2. Chop sweet potato, carrots, parsnip, and onion into 1-inch chunks. The more similar they are in size, the more evenly they will cook.
3. Add vegetables to a baking sheet and drizzle with oil, then sprinkle with garlic powder, thyme, rosemary, salt, and black pepper.
4. Toss with your hands or a large spoon to coat vegetables evenly, then spread them out in an even layer.
5. Roast for about 35-40 minutes, stirring once halfway through. Vegetables will be fork-tender when done.