In a large bowl, whisk together 2 cups apple cider, salt, thyme and rosemary. Add turkey breast and enough water to cover the bird. Cover and let brine in the refrigerator 2 hours.
Preheat oven to 425 degrees F.
For the glaze:
In a small saucepan, saute onions in oil until softened. Add peaches, honey, Worcestershire sauce, brown sugar and remaining 2 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 15 minutes until skin begins to turn golden. Reduce the oven temperature to 350 degrees F 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 165 degrees F, about 45 minutes. Let the turkey rest at least 10 minutes. Its temperature will continue to rise.