1. Preheat oven to 350°. Prepare pasta according to package directions.
2. Meanwhile, stir together chicken, cream cheese, spinach, 1 cup mozzarella cheese, and next 3 ingredients in a large bowl.
3. Cut pasta shells in half through 1 side. Fill each shell with chicken mixture, gently pressing cut sides together around filling. Place, cut sides down, in 2 lightly greased 11- x 7-inch baking dishes. Pour sauce over shells.
4. Bake, covered, at 350° for 25 minutes. Uncover and sprinkle with remaining 1 cup mozzarella cheese. Bake, uncovered, 10 to 15 minutes or until cheese is melted and cannelloni are thoroughly heated. Garnish, if desired.
Note: You can make this in a 13- x 9-inch baking dish if you don't have 2 (11- x 7-inch) dishes. Bake, covered, 30 minutes. Uncover, sprinkle with cheese, and bake 15 to 20 minutes or until cheese is melted and cannelloni are thoroughly heated.