Preheat your oven to 375°F (190°C). While it's heating, butterfly each chicken breast by cutting horizontally through the middle, being careful not to cut all the way through.

Heat 1 tablespoon of olive oil in a pan over medium heat. Add minced garlic and sauté for 30 seconds. Add spinach and cook until just wilted, about 2 minutes. Remove from heat and let cool slightly.

In a bowl, combine the cooled spinach mixture with crumbled feta, cream cheese (if using), and half of the oregano. Mix well.

Open each butterflied chicken breast and spread equal portions of the spinach-feta mixture inside. Fold the top half over to close.

Season the outside of each chicken breast with salt, pepper, and remaining oregano.

Heat the remaining olive oil in an oven-safe skillet over medium-high heat. Sear the stuffed chicken breasts for 3-4 minutes on each side until golden brown.

Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the chicken is cooked through (internal temperature should reach 165°F/74°C).

Once done, drizzle with fresh lemon juice before serving.