Put the lentils in a pot with plenty of lightly salted water. Bring to the boil, then simmer for 25-30 minutes until cooked with a little bite. (Check the package of your lentils for the exact cooking time.) Drain, dress with a drizzle of olive oil and set aside to cool.
Meanwhile, slice the aubergines in 1 cm disks. Sprinkle on salt and leave in a sieve or on some kitchen paper to drain out excess moisture. Turn the slices occasionally.
Toast the walnuts in a dry pan or the oven and break them up (or chop them). Also chop the parsley, mint, tomatoes and onion. Add everything to a mixing bowl, including the sumac, and also add the lentils when they have cooled down enough.
In a separate bowl, add all the ingredients for the tahini yoghurt dressing.
With kitchen paper, pat dry the aubergine slices (this will also get rid of excess salt). Put oil in a frying pan and when it's hot, cover the base with aubergine slices. Be careful not to overcrowd the pan. Cook for 2-3 minutes on each side, the slices should be golden and soft on the inside. Sprinkle with za'atar (or whatever spice mix you are using).
Put tabbouleh in a shallow dish, drizzle with a little bit of the sauce, and put the aubergines on top. Drizzle on some sauce again and sprinkle on some more za'atar and/or sumac to make it look pretty. Enjoy!