Cut the apples in half, remove the cores and slice thinly. Peel the apples if you prefer.
Peel the red onion and slice it into very thin strips.
In a bowl, mix the wine vinegar and sugar until the sugar has dissolved.
Add the apples and red onion to the bowl. Season with sumac.
Mix vigorously so the surfaces of the onion and apple break down slightly. The salad will start releasing juices. Let it rest at room temperature for at least 10 minutes.
Finish with finely chopped parsley just before serving.
Notes
The salad keeps well in the fridge for next day.Add a splash of olive oil if you want a softer mouthfeel.Pairs perfectly with grilled lamb, chicken, and falafel.