Before beginning, fry your eggplants in flour, as described in Recipe Notes below. Allow them to cool on the paper towel so they are easy to handle during assembly.
Preheat the oven to 400°.
Line the bottom and sides of a deep baking dish (approx. 7x11") with butter.
Place eggplant slices in a layer on the bottom of the pan.
Top with cut up canned tomatoes.
Add a pinch of dried oregano (or torn basil leaves) and salt, then add a layer of mozzarella and some grated Parmesan cheese.
Continue with these layers until you have used up the ingredients. The top layer of the dish should be eggplant.
Sprinkle the remaining Parmesan cheese on the top and dot with small amounts of butter.
Bake in the oven for 20 minutes.
After 20 minutes, remove from the oven and press the back of a wooden spoon to the dish, checking for excess moisture. If there is, drain it off with the spoon and return the dish to the oven for another 15-20 minutes.
Allow the dish to rest for at least 5-10 minutes before serving.