Place sliced onions in a bowl. Pour enough very hot water over the onions to cover. Allow to sit for about 4 to 5 minutes. Drain in a colander. Place onions on paper towels in a single layer; pat to dry. (This step helps to lessen the sharpness of the onion.)
Place onions in a mixing bowl. Toss with remaining ingredients. Taste, and adjust the seasonings if necessary. Allow the onions to sit for about 30 minutes before serving so flavors can blend. Best served at room temperature.
Notes
To Serve:This is a perfect accompaniment with your favorite kebab dish (chicken, lamb, beef, pork, lule), burger, or grilled meat, poultry or fish.If meat isn’t your thing, add the marinated red onion-sumac to a salad, cooked potatoes, or a grain dish.