Preheat oven to 425 degrees F. Coat a large roasting pan with olive oil spray.
In a small bowl, combine herbs, salt, pepper, lemon zest and optional olive oil.
Rinse turkey breast and pat dry. With your fingers, separate skin from breast meat just enough to form a pocket. (without breaking through to the other side and leaving the outside edges attached)
Rub turkey inside and under the skin with all of the herb mixture. Secure skin in place by tying turkey breast with kitchen string.
Arrange leeks and carrots in bottom of roasting pan. Lay turkey breast on top of leeks, skin side-up. Baste with combined lemon juice and chicken broth.
Roast for 20 minutes; baste turkey and vegetables with broth and pan juices. (Basting the vegetables prevents them from drying out and sticking to the pan.)
Reduce oven temperature to 325 degrees F.
Continue roasting for about 1-1/2 hours, basting turkey and vegetables with broth and pan juices, approximately every 20 minutes. Also, occasionally mix around vegetables for even roasting. Turkey breast is done when the internal temperature reaches 165 degrees F or when juices run clear when pricked with a fork. before carving.
Transfer turkey breast to a serving platter; let stand for 10 minutes before carving. Before serving, drizzle pan juices over carved turkey breast. Serve with leeks and carrots.