01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Boil jumbo pasta shells in salted water until al dente according to package instructions. 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 pepper until fully integrated.
04 - Fill each cooked shell with approximately 2 tablespoons of the prepared mixture.
05 - Spread 1 cup Alfredo sauce evenly on the bottom of the baking dish. Arrange stuffed shells in a single layer over the sauce.
06 - Pour remaining Alfredo sauce over shells. Sprinkle with remaining mozzarella and Parmesan cheeses.
07 - Cover dish with aluminum 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.