How to Make It
Preheat the oven to 425°. On a rimmed baking sheet, toss the potatoes with the olive oil and season with salt and pepper. Roast for 10 minutes, then flip the potatoes and add the chorizo. Continue to roast for 15 minutes longer, until the potatoes and chorizo are golden and tender. Carefully toss with 2 tablespoons of the vinegar and roast for 5 minutes longer, until the vinegar is reduced and the potatoes are crisp. Let cool slightly.
Meanwhile, in a small bowl, whisk the remaining 2 tablespoons of vinegar with the mustard. While whisking constantly, slowly drizzle in the sunflower oil and whisk until incorporated. Season with salt and pepper.
Arrange the potatoes, chorizo, figs, fennel and arugula on plates. Drizzle the dressing over the top. Season with salt and pepper and serve with the remaining dressing.