Preheat grill or grill pan over medium-high heat. Brush grates with oil. Boil water in large pot over high heat. Add potatoes and parboil for about 5 minutes. Drain and rinse under cold water.
Cut potatoes in half lengthwise. In a large bowl, toss potatoes in oil. Season with salt and pepper. Grill potatoes, cut-side-down, for 8 to 10 minutes, flipping halfway through, until fork-tender. Let cool for 10 to 15 minutes.
Using a measuring spoon, scoop out 1 teaspoon from the center of each half. Reserve potato flesh for filling.
In a large bowl, mash potato flesh with a fork until smooth. Fold in mayonnaise, mustard and vinegar until combined. Season with salt and pepper. Pipe filling into the cavity of each of the potato halves. Garnish with cooked bacon, chives and smoked paprika. Serve immediately or refrigerate until ready to serve.