Heat oven to 375° F.
Toss the zucchini, potatoes, 3 tablespoons of the oil, and ½ teaspoon each salt and pepper on a rimmed baking sheet. Bake (without tossing) until the vegetables are tender, 25 to 30 minutes. Let cool.
Serve the watercress topped with the pine nuts, basil, the roasted vegetables, and Burrata. Drizzle with the vinegar and the remaining tablespoon of oil. Season with ¼ teaspoon each salt and pepper.