Step 1

To make the sumac onions, in a small bowl mix the onions with 1 tablespoon olive oil, 1 1/2 teaspoons sumac, and salt. If the onions seem a little dry, add a touch more olive oil until they are glistening. Set aside.

Step 2

Put the diced cucumbers in a strainer or colander, sprinkle with 1/4 teaspoon salt and let stand over a bowl for about 10 to 15 minutes, to drain away some of the liquid. (Don't let them sit too long, though, as you don't want them to get soggy.)

Step 3

Put the tomatoes, radishes, mint, parsley, thyme, and crumbled flatbread in a large bowl. Blot the drained cucumbers with a paper or kitchen towel, then add them along with the buttermilk, 1/4 cup olive oil, lemon juice, garlic, vinegar, 1 1/4 teaspoons salt, 1 1/2 teaspoons sumac, half the sumac onions, and several good grinds of black pepper.

Step 4

Mix everything together then transfer to a serving platter. Strew the remaining sumac onions over the salad, drizzle with a little extra olive oil, and sprinkle with the remaining 1/2 teaspoon of sumac. Serve immediately.