Sprinkle the aubergine slices with salt and place them in a colander to drain for 30 minutes. Rinse, drain and pat dry with kitchen paper. If you can, grill the aubergines over a fire, after brushing the slices with olive oil on both sides. This imparts a lovely, smoky flavour. Otherwise, fry the slices in batches in half the olive oil until well browned, tender and cooked through. Add more oil if necessary; the aubergine should be translucent. Drain on kitchen paper. Remove to a dish and arrange in overlapping slices. Sprinkle with red wine vinegar and a very little salt.
Cut the tomatoes in half across the middle, turn them cut side up and sprinkle with sugar and salt. Heat the remaining oil and fry the tomatoes skin side down, over a lowish heat, for 15 minutes. Turn carefully, lower the heat a little more, and fry for a further 10 minutes, watching to see that the sugar does not burn but lightly caramelizes with the tomato juice. Spoon the tomatoes and their juices over the aubergines or tuck them in between the slices.
Whisk the harissa together with the vinaigrette ingredients and trickle it all over the salad. Scatter chopped mint leaves over everything. Serve the salad warm, with a bowl of yoghurt for added zip.