1. Cook jumbo pasta shells in salted boiling water until slightly al dente then drain and cool.

2. In a large bowl combine shredded chicken and chopped spinach.

3. In another bowl mix ricotta cheese, cream cheese, parmesan cheese, mayonnaise, egg, garlic, onion, Italian seasoning, parsley, salt and pepper.

4. Combine the chicken mixture with the cheese mixture and stir until fully blended.

5. Spread one cup of tomato sauce in the bottom of a baking dish.

6. Fill each pasta shell with the chicken and spinach mixture.

7. Arrange the stuffed shells in the baking dish in a single layer.

8. Pour the remaining tomato sauce evenly over the shells.

9. Sprinkle mozzarella cheese on top.

10. Cover with foil and bake at 375°F (190°C) for 30 minutes.

11. Remove foil and bake another 10 minutes until cheese is melted and bubbly.

12. Let the dish rest for 5 minutes before serving.