Preheat the oven to 400°F. In a small bowl combine the spinach filling ingredients (softened cream cheese, parmesan cheese, mozzarella cheese, chopped spinach, garlic, salt, garlic powder, and red pepper flakes). Stir everything together until well combined and set aside.
Next, in a small bowl combine the spices for the chicken seasoning (Italian seasoning, salt, garlic powder, paprika, and black pepper). Set aside.
Place the chicken breasts on a cutting board. Using a sharp small knife, carefully cut a slit in the side of each breast about ¾ of the way through, making sure not to cut all the way through.
Now cover the chicken breasts with the olive oil on both sides. Then divide and rub the seasoning mixture on both sides of the chicken breasts.
Next, begin stuffing the spinach and cheese filling into the pockets of each chicken breast. Divide the filling evenly between all four breasts.
Place the stuffed chicken breasts in a large 9x13-inch baking dish. Bake uncovered for 25-30 minutes or until the internal temperature of the chicken reaches 165°F.
Remove the chicken from the oven and allow it to rest for a few minutes so the juices can redistribute throughout the breast. Serve hot and enjoy!