Preheat oven to 350 degrees.
In a medium-sized bowl mix ricotta cheese, chicken, spinach, 1 ½ cups of mozzarella cheese, parmesan cheese, egg, salt and pepper until well blended.
Spread ½ cup of spaghetti sauce evenly on the bottom of a 9×13 pan.
Spoon the cheese mixture into the uncooked manicotti shells by pressing it down until is filled from one side to the other side.
Place the filled manicotti shells in the 9×13 pan.
Pour remaining spaghetti sauce over the manicotti shells. Make sure every shell is covered with sauce.
Cover with foil and bake in the oven for 55 minutes.
Remove the pan from the oven and take off the foil.
Sprinkle the remaining ½ cup of mozzarella cheese over the shells.
Bake for 5 more minutes, or until cheese is melted.
