01 - Heat the oven to 400°F.
02 - In a medium skillet, warm 1 tablespoon olive oil over medium heat, add minced garlic and sauté for 30 seconds. Incorporate spinach and cook until wilted, about 2 minutes. Remove from heat and allow to cool slightly.
03 - In a bowl, mix the sautéed spinach, crumbled feta, chopped sun-dried tomatoes (if used), parsley, oregano, and ground black pepper until evenly combined.
04 - Pat chicken breasts dry. Using a sharp knife, create a deep pocket in the side of each breast without cutting through completely.
05 - Season the exterior of each breast with salt and pepper.
06 - Fill each pocket with the spinach and feta mixture, securing with toothpicks if necessary.
07 - Place the stuffed breasts in a baking dish and drizzle with 1 tablespoon olive oil.
08 - Cook in the oven for 25 to 30 minutes, until internal temperature reaches 165°F and juices run clear.
09 - Allow the stuffed breasts to rest for 5 minutes before removing toothpicks and serving.