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