Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Peel the turnips and cut them into 1-inch cubes, and halve the radishes.
Place the chicken breast, cubed turnips, and halved radishes onto the prepared sheet pan.
In a small bowl, whisk together the olive oil, minced garlic, chopped rosemary, thyme leaves, and the juice of half a lemon.
Drizzle the herb oil mixture over the chicken and vegetables, then sprinkle with sea salt and black pepper.
Toss the vegetables and coat the chicken thoroughly to ensure everything is well-seasoned.
Roast in the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and golden.
Let the chicken rest for 5 minutes before slicing to keep it juicy, then serve alongside the roasted root vegetables.