Heat oven to 400° F. Rub the potatoes with the oil. Place them on a rimmed baking sheet and bake, turning occasionally, until tender and easily pierced with a paring knife, 65 to 75 minutes.
Meanwhile, in a medium skillet, cook the bacon over medium heat until crisp, 6 to 8 minutes. Transfer to a paper towel-lined plate. Let cool, then crumble.
Split the potatoes and, dividing evenly, top with the arugula, sour cream, and bacon.