Coat a 6-quart or larger slow cooker with cooking spray.
Add 1 pound dried ziti, 48 ounces marinara sauce, 1 (about 15-ounce) container ricotta cheese, and 1 cup of the shredded mozzarella cheese.
Stir well to combine and arrange into an even layer.
Sprinkle with the remaining 1 cup mozzarella.
Cover and cook until the pasta is cooked through and the cheese is melted, about 1 hour on the HIGH setting.
