Preheat oven to 425 degrees F. Spray an 8x8 baking pan with nonstick spray and set aside. Lay chicken on a cutting board. Cut a slit into the chicken, creating a pocket (be sure not to cut all the way through). Continue with remaining chicken. Season both sides with salt and pepper. Set cutting board aside.
In a bowl, stir together the ricotta, 1/2 cup mozzarella cheese, 1/4 cup parmesan cheese and Italian seasoning.
Spread 1 tablespoon of spaghetti sauce inside each piece of chicken. Evenly divide the ricotta mixture into 4 sections. Fill each piece of chicken with a ricotta mixture. Place in the prepared baking pan with the filled side of the chicken facing up. Gently spread 1/2 cup spaghetti sauce onto the chicken. Top with remaining mozzarella and parmesan cheese. Cover lightly with foil and bake for 25 minutes. Remove foil and bake another 15 to 20 minutes, until the chicken reaches 165 degrees. Top with fresh parsley if desired.