In a mixing bowl, combine the chopped spinach, feta cheese, sun-dried tomatoes, Kalamata olives, minced garlic, dried oregano, olive oil, salt, and pepper. Mix well until all ingredients are evenly combined.
Place the chicken breasts on a clean cutting board and slice a pocket into each breast, being careful not to cut all the way through.
Stuff each chicken breast with the Greek filling, ensuring they are generously filled. Secure the openings with toothpicks or kitchen twine to hold the filling inside.
Season the outside of each stuffed chicken breast with additional salt and pepper.
Heat a large oven-safe skillet over medium heat. Add a drizzle of olive oil and carefully place the stuffed chicken breasts in the skillet. Sear for 4–5 minutes on each side until golden brown.
Transfer the skillet to the preheated oven and bake for an additional 20–25 minutes until the chicken is fully cooked (internal temperature should reach 165°F or 75°C).
Once cooked, remove from the oven and let rest for a few minutes before carefully removing the toothpicks or twine.
Slice the stuffed chicken breasts in half to reveal the vibrant filling.
Notes
Serve on a bed of lemon-herb quinoa or alongside roasted vegetables. Garnish with fresh parsley and a lemon wedge.