Peel and wash 2-3 average size potatoes. And boil about half time until they are done. That depends from type of potatoes, but if you boil them around 20 minutes, boil only for 10 minutes (time counting is after the water boils, because only then you should put potatoes in the pot).
When they cool, slice them in 5mm slices.
Take another pan and start frying sliced zucchini. You might need to do it in few go's, because it will not fit in one. Author suggests to do the same with eggplant. But I must say I didn't like it. Eggplant absorbed a lot of oil and became very greasy. Next time I will try to grill it or even toast it.
Take 800g (2 cans) canned tomatoes, crush them with a fork. Add some salt, pepper, one spoon of oregano and basil (one spoon of each).
Separately grate 500g mozzarella cheese and 100g hard cheese, like cheddar.
That's it - all your ingredients are ready. If you are planning to bake it tomorrow keep all the parts in the fridge.
Bake for one hour in 190C celsius oven. Bon appetit!