Prepare the Filling: Heat olive oil in a skillet over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant. Add spinach and cook until wilted (about 2-3 minutes). Remove from heat and mix in the crumbled feta cheese and lemon juice. Set aside.

Prepare the Chicken: Place the chicken breasts on a cutting board. Using a sharp knife, cut a pocket into each chicken breast, being careful not to cut all the way through.

Stuff the Chicken: Spoon the spinach and feta mixture into each chicken breast pocket. Secure the openings with toothpicks.

Season the Chicken: Rub the chicken breasts with olive oil and season with oregano, salt, and pepper.

Cook the Chicken: Preheat the oven to 375°F (190°C). In an oven-safe skillet, sear the chicken breasts over medium-high heat for 2-3 minutes on each side until golden brown. Transfer the skillet to the oven and bake for 20-25 minutes or until the internal temperature reaches 165°F (75°C).

Serve: Remove the toothpicks and let the chicken rest for a few minutes before serving. Enjoy with your favorite side dishes, such as roasted vegetables or a light salad.