Pre-heat the oven to 200ºC (fan assisted)/375ºF/Gas Mark 6.
Cut the aubergines in half, lengthways and scoop out the middle of each aubergine, leaving a 2cm border. Cut the flesh into small cubes and set to one side. Place the aubergine boats onto a baking tray, brush with a little olive oil and bake for 20 minutes.
Meanwhile to make the filling, heat the remaining 2 tbsp olive oil in a large frying pan and fry the garlic for 1 minute. Stir in the reserved aubergine flesh and fry for a 10 minutes followed by the tomato passata, capers, black olives and basil. Bring to the boil and simmer for 15 minutes or until it becomes thick and pulpy.
Divide the filling between each of the four aubergines and lay the mozzarella cheese over the top. Place back in the oven for 10 minutes until the cheese has melted. Drizzle with extra virgin olive oil and serve with a salad.