Preheat the oven to 220C/gas 7. Heat some olive oil in a frying pan over a medium heat and cook the aubergine in batches, adding more oil if necessary, for 5–7 minutes, until softened and golden. Using a slotted spoon, transfer to a large bowl.
Add the onion and garlic to the pan, with a little more oil if necessary, and sauté for 5 minutes, until softened. Transfer to the bowl with the aubergine. Add the potato, tomatoes, courgette, passata and 200ml water to the bowl. Sprinkle with oregano and parsley and season generously with sea salt and ground black pepper. Combine well with your hands and transfer to a large ovenproof dish. Drizzle with any remaining oil.
Bake for 30 minutes then turn oven down to 200C/gas 6. Bake for another 20–30 minutes, or until the top has browned and vegetables are tender. Allow to cool slightly before serving.