Preheat the oven to 350 degrees.
Prepare a 9×13 casserole dish by spraying with olive oil or cooking spray. Set aside.
Cook shells to al dente (to package directions)
Drain the cooked shells and set aside to come to room temperature.
In a medium bowl, combine mozzarella & parmesan cheese. Remove half & set aside.
With the remaining half of the cheese mixture, add ricotta, egg, chicken, half the salt & pepper. Stir until fully incorporated.
Pour half the jar of the alfredo sauce into the bottom of the prepared casserole dish.
Spoon the chicken mixture into each cooked shell, about 1 heaping tablespoon into each.
Place the stuffed shells on top of the alfredo sauce in the casserole dish in a single layer.
Pour the remaining alfredo sauce over the prepared shells.
Top with remaining cheese, remaining salt and parsley (if adding)
Bake in preheated oven for 15-20 minutes, or until cheese is melted and bubbling.
Garnish with additional parsley before serving if desired.