Place the sliced eggplants in a colander, sprinkle with about a tablespoon of salt and toss well. Let drain 30 minutes.
Heat 1 tablespoon oil in a frypan and cook the onion 5 minutes until soft. Add the oregano, basil, mushrooms and tomato pasta sauce. Simmer 10 minutes and season with salt and pepper.
Rinse the eggplant slices and dry on paper towels. Place on a baking tray and brush with remaining oil. Grill under high heat 10 minutes, turning once.
Arrange 3 lasagne sheets in the bottom of a greased ovenproof dish. Spoon on 1/3 of the tomato sauce, then 1/3 of the eggplant and 1/3 of the mozzarella. Repeat twice more.
Cover with foil and bake at 190 degrees C for 45 minutes. Remove the foil after 20 minutes so the top can brown.