Summer tomato salad with sumac onions

Summer is the best time to make this salad, using an assortment of shapes, sizes and colors of fresh-picked beauties from a garden or farmers market. Likewise, make use of new crop red onions, smaller the better. Note the salad contains no vinegar or lemon juice -- it relies on powdered sumac to supply its unique sour notes. Sumac is a spice favored throughout the Middle East and one well worth having in the spice cupboard. This is a simple salad to make and delivers lots of flavor. Serve on its own or to accompany everything from roast chicken to grilled shrimp. For brightness, chop the herbs at the last minute and add just before serving.