Using a sharp knife, cut a pocket in each chicken breast by cutting horizontally through the thickest portion to, but not through, the opposite side. In a small bowl combine 1/4 cup of the feta cheese and the lemon peel. Spoon cheese mixture into each pocket. Sprinkle chicken with salt and pepper.
In a large skillet heat oil over medium heat. Add chicken. Cook for 18 to 20 minutes or until chicken is no longer pink (170 degrees F), turning once. Sprinkle with remaining feta cheese. Makes 4 servings.