Preheat the oven to 375°F (190°C).
Slice the zucchini and the tomatoes thinly and set aside.
Heat the 6 tablespoons of olive oil in a large frying pan over medium heat.
Fry the cubed eggplant, onions and mushrooms (if using) until nearly golden.
Grate in the garlic and add the oregano, a pinch of salt and a generous grinding of pepper to taste. Cook for a minute or so more.
Spread over the bottom of a 9 x 13 inch (22 x 33 cm) baking dish.
Place a layer of zucchini on top of the hot vegetables, overlapping the slices a bit like fish scales. Follow with a layer of sliced tomatoes.
Top with another layer of zucchini slices.
Cover with a lid or aluminum foil and cook for 30 minutes.
Meanwhile, mix together the breadcrumbs, cheese and parsley or chives.
When the vegetable have cooked for 30 minutes, remove the cover and sprinkle the vegetables evenly with the topping mixture.
Drizzle with 1 tablespoon olive oil.
Return to the oven for a further 10 minutes, or until the topping is crisp and golden.