Bring a pot of water to a boil and cook pasta only 6-7 minutes. It will be firm (and will soften when it's baked).
While waiting for water to boil, chop the sausages (into big pieces) and the onion and garlic. Cook together in olive oil in a skillet 3-4 minutes (they'll cook further when baked). Put sausages, onion and garlic in a large casserole dish.
In the same oil fry as many eggplant pieces as you can fit. Cook until both sides are browned and then add eggplant to casserole. Repeat with all of the eggplant pieces, adding more oil when necessary.
Add the cooked rigatoni (drained) and ½ cup of the pasta water to the casserole. Roughly chop or tear basil and add to casserole and add 1 cup of mozzarella. Grind in some black pepper. Pour in pasta sauce. Stir until all ingredients are combined.
Sprinkle remaining cup mozzarella and Parmesan over pasta. Cover with foil and refrigerate if making ahead, or immediately bake at 450 degrees for 15 minutes.