Prep the oven and pan: Preheat your oven to 400°F (200°C). Lightly oil a baking dish or line it with parchment for easy cleanup.
Make the filling: In a bowl, combine spinach, garlic, feta, cream cheese or Greek yogurt, lemon zest, lemon juice, and herbs if using. Add a pinch of salt and pepper.
Mix until creamy and evenly combined.
Season the chicken: Pat the chicken breasts dry. Drizzle with 1 tablespoon olive oil. Sprinkle with 1/2 teaspoon salt, 1/4 teaspoon pepper, and Italian seasoning on both sides.
Cut a pocket: Place a chicken breast flat on a board.
Using a sharp knife, slice horizontally into the thickest side to create a deep pocket, stopping about 1/2 inch from the opposite edge. Repeat with the rest.
Stuff securely: Spoon the spinach-feta mixture into each pocket, dividing evenly. Don’t overfill.
Secure the opening with 2–3 toothpicks to keep the filling inside.
Sear (optional but recommended): Heat a large oven-safe skillet over medium-high heat with a drizzle of oil. Sear the chicken 2–3 minutes per side until lightly golden. This boosts flavor and texture.
Bake: Transfer the chicken to the prepared baking dish (or keep it in the oven-safe skillet).
Bake for 18–22 minutes, or until the internal temperature reaches 165°F (74°C).
Rest and serve: Let the chicken rest for 5 minutes to keep it juicy. Remove toothpicks and slice. Spoon any pan juices over the top.