01 - Set the oven to 400°F and allow it to preheat fully.
02 - Heat 1 tablespoon olive oil in a 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 cool slightly.
03 - In a mixing bowl, blend sautéed spinach, crumbled feta, sun-dried tomatoes if using, parsley, oregano, and black pepper until evenly combined.
04 - Pat chicken breasts dry with paper towels. Carefully cut a deep pocket into the side of each breast, avoiding cutting through completely.
05 - Season the exterior of each chicken breast with salt and black pepper evenly.
06 - Fill each pocket with the spinach and feta mixture, securing with toothpicks if necessary to hold the filling.
07 - Place stuffed breasts in a baking dish and drizzle evenly with 1 tablespoon olive oil.
08 - Bake for 25 to 30 minutes, or until internal temperature reaches 165°F and juices run clear.
09 - Allow the breasts to rest for 5 minutes before removing toothpicks and plating.