Cut each aubergine into 8 thin slices and soak in salted water for about an hour. To make the dresssing, put the oil, lemon juice and zest and the balsamic vi8negar in a bowl and whisk well. Add the sugar and the salt and pepper to taste. Stir in the mint and set aside.
Heat a ridged stove-top grill pan until hot,drain the aubergines, pat dry with kitchen paper and brush lightly with olive oil. Add to the grill pan and cook for 2 to 3 minutes on each side until golden brown and lightly charred. Place the slices on a large platter and spoon the dressing over the top.
Cover and set aside to let the aubergines absorb the flavours of the dressing. Sprinkle with the remaining chopped mint leaves and serve.