Put the sliced onion into a bowl and add the lemon juice and a good pinch of salt. Mix well and leave to macerate for 15 minutes.
Meanwhile, preheat the grill or barbecue to high. Put all the ingredients for the kebabs into a large mixing bowl with a good pinch of salt and mix well.
Thread the meat onto flat skewers (these prevent the meat from turning when you flip them over on the barbecue) so you have a sausage shape. You should be able to make eight kebabs. Cook for 3-4 minutes on each side until charred and juicy.
Add the sumac and parsley to the macerated onions and mix well.
To serve, spread the hummus onto a serving dish. Lay the kebabs on top and pile on the onions. Serve immediately with flatbreads.