Cover the aubergine in salt. Set in a colander over the sink for 30 minutes. Rinse thoroughly and pat dry. Make a small cross incision in each tomato and cover with boiling water. Leave for 1–2 minutes, then drain, remove and discard the skin and roughly chop the flesh.
Heat the oil in a large sauté pan over a medium heat. Stir in the aubergines, peppers and onion and fry until soft. Add the tomatoes and cook until softened. Add the sugar and seasoning and remove from the heat. Set aside.
Using the remaining meat mixture, repeat the method above to make a circle the size of the dish. Moisten the edges with water and place on top of the vegetables. Press down the edges so that the meat overlaps – it will shrink slightly as it cooks. Brush with a little oil and place on a baking tray.