Boil the Potatoes: Fill a large pot with water and bring to a boil. Wash the potatoes and add them to the boiling water, cooking for 15-20 minutes until fork-tender. Drain and cool slightly before cutting into pieces.

Prepare the Vegetables: While cooling, wash and chop the cucumber, halve the cherry tomatoes, and slice the red onion. Chop the parsley.

Crumble the Feta: Crumble the feta cheese into small pieces.

Mix the Dressing: In a small bowl, whisk together olive oil, lemon juice, and Dijon mustard. Add salt and pepper to taste.

Combine Everything: In a large bowl, combine the potatoes, vegetables, crumbled feta, and dressing. Gently fold together.

Chill and Serve: Cover and chill for at least 30 minutes. Toss gently before serving and garnish with extra parsley.