Cook manicotti a couple minutes under the box instructions.
Drain in a colander, and cut manicotti in half.
Arrange manicotti tubes upright in a parchment paper-lined springform pan until the pan is packed with the tubes.
In a large bowl, combine artichokes, spinach, chicken, ricotta cheese, ½ of the mozzarella cheese, ½ of the parmesan cheese, garlic, salt, and pepper.
Preheat oven to 350°F (180˚C).
Transfer the spinach and artichoke mixture into a piping bag.
Fill each manicotti tube about ¾ of the way up with spinach and artichoke mixture.
Spoon tomato sauce over the filled manicotti.
Top with remaining mozzarella cheese, and parmesan cheese.
Cover with foil and bake 15 minutes. Remove foil and bake an additional 15 minutes or until cheese is melted.
Garnish with parsley, if desired.
