Wash the potatoes under cold running water and scrub gently to remove dirt. Place in a large pot, cover with cold water about an inch above the potatoes.

Add a generous pinch of salt, bring to a boil over medium-high heat, then reduce to medium-low and simmer for 15 to 20 minutes until fork-tender.

While potatoes are cooking, whisk together olive oil, lemon juice, sumac, salt, and black pepper in a medium bowl. Set aside.

After cooking, drain the potatoes and let cool for a few minutes. Cut into bite-sized cubes.

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

Pour the dressing over the potato mixture and gently toss to coat without mashing the potatoes.

Taste the salad and adjust seasoning if needed before serving.

Serve at room temperature or chill in the refrigerator before serving. Garnish with parsley.