In a skillet, heat olive oil over medium heat. Sauté minced garlic until fragrant, about 1 minute.
Add chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Remove from heat and allow to cool slightly.
In a mixing bowl, combine the sautéed spinach, feta cheese, cream cheese, dried oregano, lemon zest, salt, and pepper. Mix until well blended.
With a sharp knife, create a pocket in each chicken breast by slicing them horizontally, taking care not to cut all the way through.
Generously stuff each chicken breast with the spinach and feta mixture. If desired, secure the opening with toothpicks to hold the filling inside.
If using breadcrumbs, sprinkle a thin layer over each stuffed chicken breast for an extra crunch.
Place the stuffed chicken breasts in a lightly greased baking dish.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and the juices run clear (internal temperature should reach 165°F or 75°C).
Once done, allow the chicken to rest for about 5 minutes before serving.
Notes
Serve on a bed of rice or sautéed vegetables, garnished with fresh herbs.