Preheat your oven to 375°F (190°C).

In a mixing bowl, combine the chopped spinach, crumbled feta, minced garlic, olive oil, salt, pepper, dried oregano, and lemon juice. Mix everything thoroughly until well-combined.

Place the chicken breasts on a clean cutting board. Using a sharp knife, carefully cut a pocket into the side of each chicken breast, making sure not to cut all the way through.

Generously spoon the filling mixture into each pocket you cut into the chicken. Use toothpicks to secure the openings if necessary.

Arrange the stuffed chicken breasts in a baking dish and drizzle lightly with olive oil. Season with a little extra salt and pepper if desired.

Bake in the preheated oven for about 30-35 minutes, or until the chicken reaches an internal temperature of 165°F (75°C).

Let the chicken rest for a few minutes before removing from the oven. Serve hot, paired with a fresh salad or some roasted vegetables.