Preheat the oven to 200°C. Place the whole aubergine in a baking tray and roast for 25–30 minutes until blacked, and soft. Allow to cool, and peel the skin away from the flesh, roughly chop and add to a mixing bowl
Roughly blitz the pistachio in a blender and add to the mixing bowl with the aubergine. Similarly, blitz the rocket, until finely chopped and add to the pistachio and aubergine. Add garlic, lamb and season, mixing well until everything is combined.
With wet hands, divide the mixture into 8 patties (you could make them smaller if you wish).
Heat a glug of olive oil in a heavy based frying pan, over a medium heat. Cook the patties for about 5 minutes on each side, until nicely golden. Allow to rest on a board while you make the yoghurt.
For the sumac yoghurt, simply mix together the yoghurt, lemon juice, olive oil, sumac and season with salt and pepper.
Dollop the yoghurt over the patties or serve alongside as a dip.