Heat a tablespoon of olive oil in a small saucepan. Add the onion, season with a pinch of salt, and fry for 5 minutes until softened but not browned. Grate in the garlic (I love using a microplane for this) and fry for another minute or so.
Add in the chopped tomatoes and dried oregano and stir well. Bring to a simmer and continue simmering for approximately 20 minutes, until the sauce has thickened. Season well with salt and pepper and leave to cool.
Meanwhile, cut the aubergines in slices, approximately 1/2 cm thick. This recipe serves four starters, and you want to end up with approximately five slices of aubergine per tower, so make sure you have about 20 slices.
Slice the mozzarella thinly. Place the slices on some kitchen towel to remove any excess liquid.
In a large frying pan, fry the slices of aubergines for a few minutes on each side. The aubergines should soften but not brown too much. They can develop some colour, but if you feel they brown too much, lower the heat. Transfer the aubergine slices to some kitchen towel to absorb any excess olive oil which will ensure the final result isn’t too greasy. Continue cooking the aubergine in badges.
Once you have prepared all components, brush a large oven dish with olive oil and start building the four towers. Start with a slice of aubergine, add a heaped teaspoon or so on top and spread over the aubergine slice. Layer some mozzarella on top and sprinkle with some parmesan cheese. Continue in this order to build five layers, ending with some tomato sauce and parmesan cheese, no mozzarella.
Place the dish in the oven for 15-18 minutes. The mozzarella should be melted and the top turned slightly golden, but ensure not to overcook as the aubergine will go too soft risking the towers to collapse.
Leave to cool slightly before serving. Serve with some fresh basil.