01 - Set oven temperature to 400°F and lightly grease a baking dish with olive oil.
02 - Heat 1 tablespoon olive oil in a skillet over medium heat; sauté garlic for 30 seconds, then add spinach and cook until wilted, about 2 minutes. Remove from heat and let cool slightly.
03 - In a mixing bowl, combine the cooled spinach, feta cheese, cream cheese, oregano, and red pepper flakes until fully incorporated.
04 - Pat chicken breasts dry. With a sharp knife, carefully cut a horizontal pocket into each breast without slicing all the way through.
05 - Season both the interior and exterior of each chicken breast with salt and black pepper.
06 - Fill each chicken breast pocket with the spinach and cheese mixture; secure openings with toothpicks if necessary.
07 - Place stuffed breasts in the prepared baking dish and drizzle with 1 tablespoon olive oil. Bake for 25 to 30 minutes until internal temperature reaches 165°F and juices run clear.
08 - Remove toothpicks, let rest for 5 minutes, then slice and serve.