Prepare a charcoal or gas grill for direct grilling over medium-high heat.
Bring a saucepan three-fourths full of water to a boil over high heat. Add the potatoes and cook just until they can be pierced with a knife, but are not completely tender, 5 to 7 minutes. Do not overcook. Drain and pat dry. Brush the potatoes with vegetable oil.
Place the bacon in a cast-iron skillet over the hottest part of the charcoal fire or directly over the heat elements of the gas grill. Cook the bacon until crisp, 8 to 10 minutes. Transfer to paper towels to drain.
Oil the grill rack. Grill the potatoes over the hottest part of the charcoal fire or directly over the heat elements of the gas grill, turning once or twice, until tender when pierced with the tip of a knife, 15 to 20 minutes total, depending on the size of the potatoes.
Transfer the potatoes to a cutting board, let cool just until they can be handled, and then slice or cut into chunks, discarding any loose skin.
To make the mustard vinaigrette, in a small bowl, whisk together the olive oil, vinegar, mustard, pickle, salt and pepper.
In a large serving bowl, toss the warm potatoes, bell pepper, and onion with the vinaigrette until all the ingredients are evenly coated. Let stand for up to 30 minutes to blend the flavors. Crumble the bacon and mix it into the salad. Garnish with parsley. Serve at room temperature.