Thoroughly wash the potatoes under running water, scrubbing off any dirt.

Place the whole potatoes into a large pot, covering with cold water and adding a generous pinch of salt.

Bring the pot to a rolling boil over medium-high heat, then reduce to a gentle simmer for 15-20 minutes.

Remove from heat and drain once fork tender.

In a mixing bowl, whisk together olive oil, lemon juice, sumac, salt, and pepper.

Cube the boiled potatoes and place them in a large mixing bowl.

Add chopped parsley, diced onion, cucumber, tomatoes, olives, and feta to the cubed potatoes.

Drizzle the dressing over the salad and gently toss to combine without mashing the potatoes.

Taste and adjust seasoning if needed. Allow to rest at room temperature for 15 minutes before serving.