Preheat oven to 375 degrees F. Spray a baking sheet with non-stick cooking spray and set aside.
Cut a slit into the side of each chicken breast to create a pocket for the filling. (You don't want to cut all the way through.) Place the prepared chicken in a large mixing bowl, drizzle with oil, and toss to coat.
In a small bowl, combine the paprika, salt, Italian seasoning, garlic powder, and onion powder. Sprinkle over chicken and rub to make sure the outsides are seasoned.
In another mixing bowl, mix together spinach, Parmesan, mozzarella, cream cheese, and garlic until evenly combined.
Place the chicken breasts on the prepared baking sheet. Stuff each breast with 1/4 of the spinach mixture. Use a spoon or your fingers to spread the mixture evenly inside the pocket.
Bake for 30 minutes until chicken is cooked through to 165 degrees F and filling is melty.
Remove from the oven and serve immediately. You can sprinkle a little chopped parsley on top for garnish, if desired.