In a skillet over medium heat, sauté the garlic until fragrant. Add the spinach and cook until wilted. Remove from heat and let cool.

In a mixing bowl, combine the cooled spinach mixture, cream cheese, mozzarella cheese, oregano, salt, and pepper. Mix until well combined.

Preheat the oven to 375°F (190°C).

Using a knife, create a pocket in each chicken breast. Stuff each pocket with the spinach and cheese mixture.

Place the stuffed chicken breasts in a baking dish. Drizzle with olive oil and sprinkle with parmesan cheese.

Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).

Let rest for 5 minutes before slicing and serving.