First of all, sprinkle the sumac over your chopped onion, give it a squeeze and add to a small mixing bowl.
Now add your cucumber, peppers and tomato. Mix gently.
Time for the parsley and mint. Mix those, too.
Add your dressing ingredients to a ramekin dish or similar and mix before pouring over your shepherd's salad.
If you're entertaining, transfer your shepherd salad to a clean serving bowl.
