Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
Peel the carrots and parsnips, then slice them into uniform 1-inch rounds to ensure even roasting.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a large bowl, toss the root vegetables with half of the olive oil and a pinch of the salt and pepper.
Pat the chicken breast dry, then rub with the remaining olive oil, minced garlic, rosemary, and the rest of the salt and pepper.
Arrange the chicken and vegetables in a single layer on the prepared baking sheet.
Roast for 25 to 30 minutes, or until the chicken is cooked through and the vegetables are golden and tender.
Allow the chicken to rest for 5 minutes before slicing to keep it juicy, then serve immediately with the roasted roots.