Preheat oven to 400°F and line a large baking sheet with parchment paper.
Dice the chicken breast, sweet potato, carrots, and parsnips into uniform 1-inch pieces.
Mince the garlic clove finely.
In a large bowl, combine the diced chicken, vegetables, garlic, olive oil, rosemary, thyme, salt, and pepper.
Toss everything together until the ingredients are evenly coated with the oil and herb mixture.
Spread the mixture in a single layer on the prepared baking sheet, ensuring space between pieces for even browning.
Roast for 25-30 minutes, tossing halfway through, until the chicken is cooked through and the vegetables are tender and golden.