01 - Preheat oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
02 - Cook pasta shells according to package instructions until al dente. Drain, rinse with cold water, and set aside.
03 - In a large mixing bowl, combine cooked chicken, ricotta, spinach, mozzarella, Parmesan, egg, garlic, salt, pepper, and Italian herbs. Mix until well combined.
04 - Spread 1 cup of Alfredo sauce evenly over the bottom of the prepared baking dish.
05 - Fill each cooked shell with about 2 tablespoons of the chicken-spinach mixture and arrange in the baking dish, open side up.
06 - Pour the remaining Alfredo sauce evenly over the stuffed shells.
07 - Sprinkle with mozzarella and Parmesan cheese for the topping.
08 - Cover the dish with foil and bake for 25 minutes.
09 - Remove foil and bake an additional 10 minutes, or until cheese is golden and bubbly.
10 - Garnish with chopped parsley if desired. Let rest for 5 minutes before serving.