Chicken and Spinach Pasta Bake

I made this tonight and it was good.  Nice weeknight meal, and easily gluten free.  Kids all enjoyed it.  Success.  Yay!  Thank you, pinterest.  

• 8 oz uncooked rigatoni pasta (I used gluten free)
• 1 TBS olive oil
• 1 cup finely chopped onion (I used red onion)
• 1 10 oz package frozen chopped spinach, thawed (I used fresh spinach, didn't chop or anything)
• 3 cups cooked cubed chicken breast
• 1 14 oz can Italian diced tomatoes, undrained
• 1 8 oz container chive and onion cream cheese
• 1/2 tsp salt
• 1/2 tsp pepper
• 1 1/2 cups shredded mozzarella cheese

1. Preheat oven to 375.
2. Prepare rigatoni according to package directions.
3. Spread oil on bottom of a 11x7 baking dish.  Layer on the onion and bake at 375 for 15 mins, or until tender.
4. Transfer the onion to a large bowl, and mix with remaining ingredients, except for the mozzarella cheese.  Spoon mixture into baking dish and top with cheese.  Cover and bake at 375 for 30 minutes.  Uncover and bake an additional 15 minutes until bubbly.