Slice the eggplant (1 cm/0.5 inch tall). Sprinkle them with salt and place them in a colander for about 15 minutes.
Slice the mozzarella and set it, to eliminate the extra liquids, in another colander or sieve.
Grill the eggplant slices on a hot grilling pan, brushed with a teaspoon of olive oil.
Grill 6-8 minutes per side until well done.
Remove the garlic and add the passata. Cook over medium/low heat for 20 minutes. Add a pinch of salt and mix.
Turn the heat off and add the basil leaves. Mix and let rest.
Anyway, what you have to do to assemble the dish is the following:
Spread the bottom of the casserole with a thin layer of the tomato sauce and add a layer of eggplant slices.
Cover with a layer of sauce, a layer of mozzarella, and another of parmesan cheese.
Add another layer of eggplant. You might want to place some vertically and some horizontally, or just enough slices to cover the surface.
Cover with tomato sauce, add a layer of mozzarella and another of parmesan.
Finally, add a last layer of eggplant, cover it with sauce and finally, sprinkle it with parmesan.
Summarizing: sauce + eggplant + sauce + mozzarella + parmesan + eggplant + sauce + mozzarella + parmesan + eggplant + sauce + parmesan.