Mix all of the seasoning ingredients together and set aside.
Roughly chop the baby spinach and place it into a mixing bowl. Add the cream cheese, feta, and mozzarella. Massage the spinach with your hands, until well combined (it should look like thick paste).
Using a sharp knife, cut a pocket into the side of each chicken breast.
Divide the spinach stuffing into four equal parts and spoon it into the chicken pockets. Using toothpicks, secure the stuffing inside.
Generously season the chicken with the spice mix and brush with olive oil on both sides.
Bake the chicken in a preheated oven at 400ºF for 25-30 minutes, depending on how large your chicken breasts are.