Carefully slit lengthwise pocket in chicken breasts, starting at the thick side and cutting approximately 3/4 of the way through the width of each breast. Season inside and out with salt and pepper and set aside.
In large bowl make the stuffing by combining the ricotta with the black olives, onion, parsley and garlic salt. Place about a 1/4 cup of stuffing in each pocket of the chicken breasts.
Arrange the chicken in a 9X13" baking pan and cover with the pasta sauce. Bake uncovered at 350 degrees about 35-40 minutes, or until the chicken is done. Sprinkle the mozzarella over the top and return to the oven another 2-3 minutes until the cheese is melted.
Serve the chicken on top of the fettucini. If you prefer more sauce, you can spoon some of the additional sauce from the baking dish over the pasta as well.