1. Preheat the oven to 425°F and position the oven rack in the center.

2. In a medium bowl, combine the cream cheese, mayonnaise, garlic, and salt until smooth. Stir in the mozzarella, Parmesan, and chopped spinach until fully mixed.

3. Place the chicken breasts on a cutting board. Using a sharp knife, cut a pocket into the side of each breast, slicing about three-quarters of the way through without cutting all the way.

4. Divide the filling evenly among the chicken breasts and stuff each pocket. Secure the openings with toothpicks if needed.

5. In a small bowl, mix together the salt, black pepper, garlic powder, and paprika. Season the chicken on all sides.

6. Heat olive oil in a large oven-safe skillet over medium heat. Add the stuffed chicken breasts and cook for about 4 minutes per side until golden brown.

7. Transfer the skillet to the oven and bake for 10 to 15 minutes, or until the internal temperature reaches 165°F.

8. Remove the chicken from the oven and let it rest for 5 minutes before serving. Spoon the pan juices over the top for extra flavor.