In a large skillet over medium heat, add 1 tablespoon of olive oil.
Once hot, add the minced garlic and chopped spinach, sautéing until the spinach wilts (about 2-3 minutes).
In a mixing bowl, combine the sautéed spinach, feta cheese, cream cheese, dried oregano, lemon zest, salt, and pepper. If using, also mix in the sun-dried tomatoes. Stir well until the mixture is smooth and combined.
Take each chicken breast and make a pocket by slicing horizontally through the thickest part, ensuring you don't cut all the way through.
Stuff each pocket generously with the spinach and feta filling. You can use toothpicks or kitchen twine to secure the openings if needed.
Season the outside of the stuffed chicken breasts with salt and pepper.
In the same skillet, add another tablespoon of olive oil, and sear the chicken breasts over medium-high heat for about 4-5 minutes on each side until golden brown.
Transfer the seared chicken to a baking dish. If desired, sprinkle breadcrumbs on top for added crunch.
Bake in the preheated oven for 20-25 minutes, until the chicken is cooked through and reaches an internal temperature of 165°F (75°C).
Remove from oven and let rest for 5 minutes before serving.
Notes
Serve on a bed of sautéed vegetables or with a side of rustic bread. Garnish with fresh herbs for a pop of color.