01 - Preheat oven to 400°F. Lightly grease a baking dish or line with parchment paper.
02 - In a large skillet over medium heat, add 1 teaspoon olive oil. Sauté spinach for 2 to 3 minutes until wilted. Remove from heat, let cool slightly, squeeze out excess moisture, and chop finely.
03 - In a mixing bowl, combine chopped spinach, feta cheese, cream cheese, minced garlic, dill, lemon zest, and ground black pepper. Blend thoroughly until well incorporated.
04 - Pat chicken breasts dry. With a sharp knife, make a deep pocket in the side of each breast without cutting through completely.
05 - Season both sides of the chicken breasts with kosher salt and freshly ground black pepper.
06 - Fill each chicken breast with the spinach-feta mixture. Secure the opening with toothpicks if needed.
07 - Heat remaining olive oil in a large oven-safe skillet over medium-high heat. Sear stuffed chicken breasts for 2 to 3 minutes per side until golden brown.
08 - Transfer skillet to oven or place chicken in prepared baking dish. Bake for 18 to 22 minutes until the chicken is fully cooked and reaches an internal temperature of 165°F.
09 - Allow cooked chicken to rest for 5 minutes. Remove toothpicks, slice, and garnish with chopped parsley and lemon wedges if desired.