Heat the oven to 200C/fan 180C/gas 6. Cut the courgettes in half lengthwise, then scoop out the centre of the courgette to make a 1cm deep shell. Roughly chop the the scooped out courgette and keep for the filling. Put the courgette shells onto a baking tray, drizzle with 1 tsp oil, season and roast for 10 minutes until just softening. Fry the onion and garlic for 5 minutes in 1 tsp oil until soft, then add the aubergine, red pepper and chopped courgette. Cook for another 10 minutes, then add in the tomatoes and thyme and simmer for 10 minutes until thickened. Spoon into the hollowed courgettes, and dot over the mozzarella. Roast for 10 minutes until the cheese has melted and the courgettes have softened completely. Serve with any remaining veg.