Sweet Potato Salad

Preheat oven to 425 degrees F. Toss sweet potatoes, 2 tablespoons oil, 1/2 teaspoon salt and pepper in a large bowl. Divide the sweet potatoes among 2 rimmed baking sheets. Roast, stirring once halfway through, until the potatoes are softened and beginning to brown, 20 to 25 minutes. Let cool to room temperature.

Meanwhile, whisk together vinegar, mustard, sugar, the remaining 2 tablespoons oil and the remaining 1/4 teaspoon salt in a large bowl. Add the roasted sweet potatoes and arugula; toss to coat.