01 - Preheat oven to 400°F.
02 - Heat olive oil in medium skillet over medium heat. Add minced garlic and cook for 30 seconds. Add chopped spinach and sauté until wilted, about 2 minutes. Remove from heat and allow to cool slightly.
03 - In a mixing bowl, combine sautéed spinach, crumbled feta, sun-dried tomatoes if using, parsley, oregano, and black pepper. Stir thoroughly.
04 - Pat chicken breasts dry. Using a sharp knife, cut a deep pocket into the side of each breast being careful not to cut through completely.
05 - Season the outside of each breast evenly with salt and black pepper.
06 - Fill each pocket with the spinach and feta mixture. Secure openings with toothpicks if necessary.
07 - Place stuffed breasts into a baking dish and drizzle with olive oil.
08 - Bake in preheated oven for 25 to 30 minutes, until chicken reaches an internal temperature of 165°F and juices run clear.
09 - Allow chicken to rest for 5 minutes before removing toothpicks and serving.