Boil the Potatoes: In a large pot, bring salted water to a boil. Add baby potatoes and cook for about 7 minutes until tender but firm. Drain and let dry slightly.
Smash the Potatoes: Preheat your oven to 425°F (220°C). Place potatoes on a baking sheet lined with parchment paper. Gently smash each potato using the bottom of a glass until slightly flattened.
Season & Roast: Drizzle with olive oil, salt, black pepper, and vinegar (if using). Roast for 45-50 minutes, flipping halfway through, until crispy and golden.
Prepare the Dressing: In a small bowl, whisk together Greek yoghurt, mayo, Dijon mustard, lemon juice, vinegar, dill, parsley, and onion powder. Mix well and refrigerate for 30 minutes.
Prepare the Veggies: Dice cucumber, shallot, and pickles. Stir into the chilled dressing just before serving.
Serve & Enjoy: Drizzle creamy dressing over crispy potatoes and garnish with fresh parsley. Serve immediately.