Combine spaghetti sauce mix, tomato sauce, water, seasoned salt and onion in a saucepan; bring to a boil.
Reduce heat and simmer, uncovered, 20 minutes.
Peel aubergine; cut in 1/4-inch slices.
Saute aubergine slices in hot oil in a skillet until brown, adding oil as needed; drain well on paper towels.
Pour a third of the sauce into a 8-inch-square baking dish; cover the sauce with half the aubergine and mozzarella slices.
Repeat layers, ending with sauce; top with Parmesan cheese.
Bake, uncovered, in preheated 350'F. oven about 20 minutes.