Finely dice the tomatoes, cut the onion into fine strips. Make a marinade from lemon juice, olive oil and sumac. Mix everything well with the chickpeas and let it steep a little.
Salt and pepper the chicken breasts, fry in olive oil.
Mix the yogurt with the lemon juice and the sumac. Season to taste with salt and pepper.
Place the chickpea salad on a platter. Slice the chicken breast diagonally and place a ring around the chickpea salad. Cover with the yogurt.