Using a sharp knife, cut a pocket in each chicken breast by cutting horizontally though 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 18-20 minutes until internal temperature reaches 170 degrees, turning once. Sprinkle with remaining feta cheese.