In a large bowl, combine the ricotta, 1/2 cup mozzarella cheese, Parmesan cheese, spinach, chicken and egg until well combined.
Season with salt and pepper.
Transfer the filling to a large ziplock bag. Seal the bag and cut a 1/2-inch snip from
the bottom corner of the bag. Push the filling down towards the opening. Twist the
bag on top and fill each manicotti shell with filling.
Pour 3/4 cup of the Alfredo sauce over the bottom of a 9" x 13" casserole dish. Carefully
place the filled shells in the dish. Pour the rest of the sauce on top of the shells
and sprinkle the top with 1/4 cup mozzarella cheese. Bake in the oven for 45 minutes