Preheat the oven to 375°F. Trim any visible fat from the turkey breast, and save the neck, if included, for making gravy. Pat the turkey breast dry with paper towels. Place a rack in a roasting pan and set the turkey breast on the rack.
In a 2-cup glass measure, thoroughly combine the lemon juice, olive oil, rosemary, and thyme. At the top of the breast, slide your fingers back and forth under the skin to separate it from the breast meat, creating a pocket over the entire breast. Pour half the mixture inside this pocket, and the rest over the turkey breast, coating it well. Season the turkey with salt and pepper to taste. Set the turkey breast on the rack, skin-side up. Place the roasting pan in the lower third of the oven.
Roast the turkey breast, basting every 30 minutes, until the juices run clear when a sharp knife is inserted into the thickest part of the breast, or when an instant-read thermometer, inserted in the same spot and not touching bone, registers 165°F, about 1¼ to 1½ hours. Remove the turkey breast from the oven, place on a carving board, cover the breast loosely with aluminum foil, and let rest for 10 minutes.
TO MAKE THE GRAVY
While the turkey is resting, make a quick gravy. In a small jar with a tight-fitting lid, mix together the flour and 2 tablespoons of the chicken stock. Place the roasting pan over medium heat, add the remaining stock to the pan, and bring to a simmer. Using a wooden spoon, scrape and loosen any brown bits sticking to the bottom and sides of the pan. Shake the flour mixture again and add to the stock in the pan. Stir until the gravy is smooth and thickened; then ladle into a gravy boat or small bowl.
Carve the turkey breast and serve, accompanied by the gravy.