01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Cook the jumbo pasta shells in salted boiling water until al dente according to package directions. Drain and arrange shells on a baking sheet to cool.
03 - In a large bowl, mix shredded chicken, ricotta, cooked spinach, mozzarella, Parmesan, egg, garlic, Italian herbs, salt, and pepper until fully combined.
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. Place stuffed shells in a single layer over the sauce.
06 - Pour the remaining Alfredo sauce evenly over the stuffed shells. Sprinkle with the remaining mozzarella and Parmesan cheeses.
07 - Cover loosely with aluminum foil and bake for 25 minutes.
08 - Remove foil and continue baking for an additional 10 minutes until cheese is bubbly and golden.
09 - Allow the dish to rest for 5 minutes before garnishing with chopped fresh parsley and serving.