Wash the potatoes thoroughly under cold running water, using a vegetable brush to scrub away any dirt.

Place the whole, unpeeled potatoes in a large pot, cover with cold water, and add a pinch of salt. Bring to a boil over medium-high heat, then reduce to a simmer and cook for 15 to 20 minutes until fork-tender.

Let the potatoes cool slightly in the pot for about 5 minutes.

In a small bowl, whisk together the extra-virgin olive oil, lemon juice, sumac, salt, and black pepper until smooth.

Cut the cooled potatoes into bite-sized cubes.

In a large mixing bowl, combine the cubed potatoes, chopped parsley, diced red onion, cucumber slices, tomatoes, black olives, and feta cheese.

Drizzle the dressing over the potato mixture and gently toss to coat.

Taste and adjust seasoning as needed with additional salt, pepper, or lemon juice.

Serve immediately or chill in the refrigerator for about 30 minutes before serving.