01 - Preheat oven to 375°F.
02 - In a small bowl, mix olive oil, rosemary, lemon zest, lemon juice, garlic, salt, and pepper to create a fragrant marinade.
03 - Pat turkey breast dry with paper towels. Rub the marinade evenly over the entire turkey, working underneath the skin when possible. Allow to marinate for at least 15 minutes, or refrigerate overnight for enhanced flavor penetration.
04 - Arrange carrots, parsnips, and red onions in a large roasting pan. Drizzle with olive oil, season generously with salt and pepper, and toss to coat evenly. Distribute lemon slices throughout the vegetables.
05 - Place the marinated turkey breast on top of the vegetables, skin-side facing up.
06 - Roast for 1 hour 20 minutes to 1 hour 30 minutes, or until the turkey reaches an internal temperature of 165°F and juices run clear. Baste the turkey with pan juices halfway through the cooking process.
07 - If additional crisping is desired, broil on high for 2–3 minutes, watching carefully to prevent burning.
08 - Remove turkey from oven and let rest for 10 minutes before slicing to allow juices to redistribute.
09 - Slice turkey and arrange over roasted vegetables. Garnish with fresh rosemary sprigs and lemon wedges if desired.