Place the potatoes in a large pot covered with water. Season generously with salt and bring to a boil over high heat. Simmer for about 7 minutes or until the potatoes are tender but not falling apart. Drain the water and allow the potatoes to cool.
When the potatoes are cool, split each in half and add to a large bowl. Drizzle with extra-virgin olive oil and a pinch of salt and toss to coat.
In a large bowl, combine the remaining olive oil, mustard, vinegar, a pinch of salt and a few generous grinds of pepper. clean and chop the dill fronds and stems and set aside. Slice the radishes into coins.
Preheat your Spark to 450°F and brush the grill grates with oil.
Place the potatoes cut side down on the grill, turning to cook both sides evenly until crispy brown, 10-15 minutes.
Remove the potatoes from the heat and add to the bowl with the dressing. Add the dill and radishes and gently stir with a large spoon to coat the potatoes evenly with the dressing. Finish with a pinch of sea salt and serve right away.