Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Dice the chicken breast, sweet potato, carrots, and parsnips into uniform 1-inch cubes to ensure everything cooks at the same rate.
In a large mixing bowl, combine the diced chicken and vegetables, then drizzle with olive oil and sprinkle with rosemary, garlic powder, salt, and pepper.
Toss the mixture thoroughly until every piece is evenly coated in oil and seasonings.
Spread the ingredients in a single layer on the prepared baking sheet, making sure not to overcrowd the pan so the vegetables roast rather than steam.
Roast for 25 to 30 minutes, tossing halfway through, until the vegetables are fork-tender and the chicken is cooked through to 165°F.
Remove from the oven and serve immediately while the edges are perfectly crisp and golden.