Preheat the oven to 375 degrees F. Bake thepotatoes until they can be just piercedwith a knife, about 45 minutes. Cut intolarge chunks.
Preheat a grill to high. Brush the potatoes and scallions with 1/3 cup olive oil and arrange on the grill. Grill the potatoes until just tender, about 5 minutes per side. Grill the scallions until softened and marked,about 1 minute per side. Remove the scallions and potatoes from the grill; cut the scallions into small pieces.
In a large bowl, whisk the remaining 1/3 cup olive oil, the mustard, vinegars and honey; season with salt and pepper. Add the potatoes, scallions and parsley and toss until the potatoes are well coated.