Combine all the ingredients for the dressing and allow to sit at room temperature for 30 minutes to blend the flavors.
In a bowl, toss the potatoes and onions in the oil. Place the potatoes in a vegetable basket and place on the grill. Grill for about 15 minutes over a medium fire, shaking the basket often and watching for flare-ups from the olive oil. Add the onions and grill for 5 more minutes. Remove from the grill and chop the onions.
In a bowl, combine the potatoes, onions, and chile with the dressing until coated. Add the remaining ingredients, toss to mix and serve.