Put the pieces of lamb in the bowl of the robot. Mix them in fits and starts. Put the minced meat in a salad bowl. Mix with finely chopped onions, egg, chopped herbs and cumin. Salt, pepper. Divide into small portions. Shape them in rolls between your hands. Thread them on skewers. Oil them lightly.
Cut the eggplants at each end and then into thick slices. Brush with olive oil on both sides. Grill for 6 minutes per side. Salt, pepper.
Also grill kefta skewers for 5 to 6 minutes, turning them over. Place each on the eggplant slices.
The sauce: mix the yogurts beaten with the pressed garlic, the juice of the half-lemon, the harissa, the chopped mint, salt and pepper.