Slice the aubergines into 5mm discs, heat a large frying pan and add a drizzle of oil, not much then lightly fry the aubergine discs for a couple of minutes each side until golden brown, remove and put to one side whilst you brown the remaining.
In another frying pan add the pancetta and fry, it will release a lot of oil, add the mushrooms to the pan and continue frying until soft.
In a saucepan heat some more oil and add the garlic, let it sizzle for a few seconds before adding the chopped onions fry for a few minutes until soft then add the tomatoes or passata, let it bubble away for a while before adding the pancetta and mushrooms. Season and add the herbs to taste. Simmer for 10 minutes.
In an oven dish place a spoonful or two of tomato mix then layer up with aubergines and some ripped up mozarella. Repeat, but finish with a layer of aubergines.