Wash the potatoes under cold running water using a scrub brush to remove dirt.

Place the washed potatoes into a large pot filled with salted water and boil for 15-20 minutes.

Combine olive oil, lemon juice, sumac, salt, and pepper in a small bowl and whisk to blend.

Drain the potatoes and allow them to cool for about 10 minutes.

Cube the cooled potatoes into bite-sized pieces.

In a large mixing bowl, combine cubed potatoes, parsley, red onion, cucumber, tomatoes, olives, and feta.

Drizzle the dressing over the salad and toss gently to coat.

Adjust seasoning to taste with salt, pepper, or lemon juice.

Serve at room temperature or chill in the refrigerator for about 30 minutes before serving.