In a large bowl, whisk together 500ml apple cider, salt, thyme and rosemary. Add turkey breast and enough water to cover the bird. Cover and let brine in the refrigerator for two hours. Preheat oven to 220°C.
For the glaze: In a small saucepan, saute onions in oil until softened. Add peaches, honey, Worcestershire sauce, brown sugar and remaining two tablespoons apple cider. Bring to a boil. Lower to a simmer and cook until peaches break down and glaze thickens, about 12 minutes.
Remove turkey from brine and pat dry with paper towels. Brush with oil and season with pepper. Place turkey in a roasting pan. Cook for fifteen minutes until skin begins to turn golden. Reduce the oven temperature to 200°C and brush the top generously with the glaze. Continue cooking until an instant-read thermometer inserted in the thickest part of the breast reaches an internal temperature of 75°C, about 45 minutes. Let the turkey rest at least 10 minutes. Its temperature will continue to rise.