I got the original recipe for this from Ruth, but I've modified it a bit. This recipe tastes similar to lasagna and makes around 6 servings.
26 oz jar spaghetti sauce
8 oz ziti or mostaccioli pasta, uncooked
12 oz mozzarella cheese, shredded
16 oz. ricotta cheese
1/4 cup Parmesan cheese, grated
1/2 - 1 cup spinach, finely chopped (I use a food processor)
Preheat oven to 350°F. Lightly grease a 2-1/2 quart baking dish. Place half of the pasta in the bottom of the pan. Cover with half of the sauce. Sprinkle half of the mozzarella on top. In a separate bowl, beat the egg. Stir in the ricotta, Parmesan and spinach. Spread over mozzarella. Place remaining pasta on top of ricotta mixture. Cover with other half of sauce, then other half of mozzarella. Bake for 1 hour at 350°F.