Preheat the oven to 375 degrees F (190 degrees C). Spray a casserole dish with cooking spray.
Cut a shallow slice lengthwise down the middle of the top of each chicken breast using a sharp knife, starting and ending about 1 inch from the end. Partially fold the chicken breast in half along the slice to continue shallow, horizontal slices on both sides; slices should resemble an upside-down capital T.
Spread 1/4 of the ricotta cheese into each pocket. Place string cheese and pesto over ricotta. Season outsides of breasts with garlic salt, black pepper, and cantanzaro herbs.
Place chicken in the prepared casserole dish and cover with aluminum foil.
Bake in the preheated oven for 25 minutes. Remove foil and bake until chicken is no longer pink in the center and the juices run clear, about 10 more minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
