Cut the eggplants crosswise into thin slices. Arrange in a colander and sprinkle with salt. Let stand for about 30 minutes to release the bitter juices. Rinse under cold running water. Pat dry with paper towels.
Heat half the olive oil in a large saucepan. Add the onion and garlic and cook till tender. Add the undrained tomatoes, tomato paste, basil and oregano and bring to boiling. Simmer for 30 minutes, or until well thickened. Add salt and pepper.
In a large frying pan, heat the remaining olive oil. Working in batches, fry the eggplant slices on both sides until cooked through and lightly golden. Add more oil as necessary. Drain the eggplant slices on paper towels.
In a large saucepan or pasta pot bring 12 cups water to boiling. Add pasta. Reduce heat slightly. Boil, stirring occasionally, uncovered, for 14 to 15 minutes, or until al dente. (or follow pkg. directions) drain, add to tomato sauce.
To assemble, grease a 2 qt. baking dish. Arrange the ingredients in the dish in the following sequence. One third egg plant slices, half tomato pasta sauce, one third eggplant slices, half the mozzarella slices, half tomato sauce, one third eggplant slices, half mozzarella slices.
Bake, uncovered, in a preheated 350F oven for 30 minutes, or until the cheese on top is melted and golden.