Cook shells and chicken first (reserve broth from cooking chicken). Prepare stuffing mix according to package directions. Combine stuffing with chicken and mayonnaise; mix well. Stuff shells.
Blend chicken soup with the broth from cooked chicken. Pour small amount to cover entire bottom of large baking pan. Place each shell close together. Pour remaining soup mixture over shells. Sprinkle with grated parmesan cheese.
Cover with aluminum foil and bake at 350 degrees F for 35 minutes. Makes approximately 30 shells.