Easy Weeknight Lasagna in the Slow Cooker 1-2 pkgs ravioli (depends on size of raviolis) 1 16oz jar spaghetti sauce 2-3 cups shredded mozzarella cheese Spray a 5-6 qt slow cooker with non-stick cooking spray. Spoon a little sauce to cover the bottom lightly. Add layers of ravioli, sauce, and cheese. Repeat layers until slow cooker is about 3/4 of the way full. Turn on low and cook for 3-4 hours.