Warm potatoes and cool greens are a perfect combination for a late-summer meal.
Heat oven to 375 degrees. Arrange potatoes in a roasting pan and add 1 tablespoon olive oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper; rollpotatoes to coat. Roast until potatoes are tender, about 40 minutes. Remove from oven and let stand just until cool enough to handle.
Meanwhile, whisk together lemon juice, vinegar, remaining 2 tablespoons olive oil, and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper in a medium bowl; set aside.
Break each warm potato in half and place in a serving bowl. Add the vinaigrette and toss to coat. Add watercress and lemon zest, toss, and serve immediately.
