To make a stuffed chicken parmesan sub, you will first need to prepare the filling. Place the chicken breasts, skin-side down, in the bottom of an 8 x 8-inch baking dish. Fill each cavity with 1 tablespoon of the ricotta cheese, 1 teaspoon of parsley, and 1 tsp. of thyme. Cover the dish with plastic wrap and refrigerate for at least 1 hour. Preheat the oven to 450 degrees F (232 degrees C). Line the baking sheet with foil and brush with nonstick cooking spray. Bake for 20 to 25 minutes, or until chicken is no longer pink. Remove from oven and allow to rest for 5 minutes before serving.