Preheat oven to 375
prepare rigatoni as directed on package, apply cooking spray
to and 11x7 inch baking pan. Layer the chopped onion in the
baking pan and bake for 15 minutes or just until tender.
Transfer cooked onion to large bowl, press the drained
spinach dry with paper towels to remove excessive moisture.
Add cooked rigatoni, spinach, chicken, diced tomatoes,
cream cheese, sun dried tomatoes and pepper to the bowl
with the onions and mix well. Spoon mixture into the baking
pan and sprinkle evenly with shredded mozzarella cheese.
Bake covered for 30 minutes and uncover and bake an
additional 15 minutes