Preheat the oven to 350 degrees.
Spray a Corningware or Pyrex dish with non-stick spray.
Add the ziti to the dish.
In a separate bowl, use a food processor or a hand immersion blender to combine the ricotta and the spinach.
Combine that and the sauce into the ziti, and mix well.
Sprinkle the mozzarella cheese on top.
Cover and cook for 25 minutes.
Remove cover and cook another 10 minutes. Serve immediately.
** Can also make with no-boil lasagna noodles and cook for 45 minutes, covered before adding mozzarella cheese.