Onions peel and cut into slices. Wash the tomatoes and cut into very thick slices. Dab meat dry. Roll up the slices from the short side, then halve each slice. Put meat rolls, onions, tomatoes and olives alternately on skewers.
For the marinade, halve the lime and squeeze the juice. Mix lime juice, harissa and oil. Season with 1⁄4 TL coriander and well 1⁄2 TL cumin. Spread a thin layer on all sides of the skewers, cover and chill for about 1 hour.
Then season the skewers with salt. Grill on the hot grill for about 15 minutes, turning. In the meantime, spread the rest of the marinade over and over again.