01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Boil jumbo pasta shells in salted water until al dente following package directions. Drain and spread shells on a baking sheet to cool.
03 - In a large bowl, mix chicken, ricotta, spinach, mozzarella, Parmesan, egg, garlic, Italian herbs, salt, and black pepper until fully blended.
04 - Fill each cooked shell with approximately 2 tablespoons of the chicken mixture.
05 - Spread 1 cup Alfredo sauce evenly on the bottom of the prepared baking dish. Arrange stuffed shells in a single layer over the sauce.
06 - Pour remaining Alfredo sauce evenly over the shells, then sprinkle with the remaining mozzarella and Parmesan cheeses.
07 - Cover the dish with foil and bake for 25 minutes.
08 - Remove foil and bake an additional 10 minutes until cheese is bubbly and golden.
09 - Allow to rest for 5 minutes before garnishing with fresh parsley and serving.