small onion, chopped
Sauté onion in olive oil until it's nice and clear.
Add the tomato paste, tomato sauce, water, oregano, basil, salt and pepper. Oh, my - doesn't it smell good?! Simmer this on low for about 10 minutes.
In the meantime, preheat your oven to 375 degrees and make sure your ziti is drained fully.
Grease a 1-1/2 quart casserole. I, personally, like the non-stick sprays.
In a small bowl, combine your mozzarella & ricotta cheeses.
Take your casserole dish, put it on a heat safe surface. Now, put in 1/2 of your ziti, put 1/2 of your sauce on top of that, and add a layer of 1/2 of the cheese. Repeat and top with the cheeses.
Bake for 25-30 minutes.