Preheat the oven to 375°F (190°C).
Trim excess fat from 4 boneless, skinless chicken breasts.
Cut a pocket into each chicken breast, being careful not to cut all the way through.
In a mixing bowl, combine 2 cups of chopped spinach and 1 cup of crumbled feta cheese. Optionally, sauté the spinach in olive oil before mixing.
Generously stuff each chicken breast with the spinach and feta mixture.
Secure the pockets with toothpicks if necessary.
Heat 2 tablespoons of olive oil in an oven-safe skillet over medium-high heat.
Sear the chicken breasts for 3-4 minutes on each side until golden brown.
Transfer the skillet to the oven and bake for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Let the chicken rest for a few minutes before serving.
Garnish with fresh parsley (optional) and serve with your favorite sides.