1. Preheat the grill to medium. Put the red potatoes in a large saucepan and cover with cold water by 2 inches. Bring to a boil over high heat. Once water begins to boil, about 10 minutes, add the sweet potatoes. Return to boil and cook 10 minutes longer. Drain and set aside to cool.

2. In a medium bowl, whisk the mayonnaise, mustard, onion powder, garlic powder, cayenne, salt and pepper. When potatoes are cool to touch, gently toss in the mixture to coat..

3. Make the vinaigrette: cook the bacon in small skillet until crisp, then set pan aside to cool. Once cool, pour the bacon and drippings into a small bowl with the olive oil, whisking to emulsify. Add the scallions, parley, salt & pepper. Whisk to blend.

4. Using tongs, place the potato pieces on the hot grill and cook on all sides long enough to cook through. Handle gently so the potatoes don’t fall apart. Remove and place into bowl with vinaigrette. Gently toss to coat and serve warm or cold.