Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the carrots and parsnips, then chop them into uniform 1-inch chunks to ensure they cook at the same rate.
Place the chicken breast and the chopped root vegetables onto the prepared baking sheet.
Drizzle the olive oil over the chicken and vegetables, then sprinkle evenly with the dried rosemary, sea salt, black pepper, and garlic powder.
Toss the vegetables with your hands or a spatula to coat them thoroughly in the oil and spices, and flip the chicken to season both sides.
Spread the ingredients into a single layer, ensuring the chicken is in the center of the tray surrounded by the vegetables.
Roast in the oven for 25 to 30 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are fork-tender and slightly caramelized.
Remove from the oven and let the chicken rest for 5 minutes before slicing to keep the meat juicy and tender.