Transfer to a bowl of ice water to cool. Peel and slice potatoes 1/2-inch thick; reserve.
With a sharp knife, remove peel and thick white pith from oranges; reserve juice in a bowl. Halve and slice crosswise into 1/2-inch-thick half moons, reserving juice.
Transfer 3 tablespoons of collected juice into a bowl; whisk in vinegar, sesame oil, soy sauce, and salt; reserve.
Spray grill pan with cooking spray; heat over medium-high until hot. Cook potatoes until grill marks appear, turning once (3-5 minutes per batch).
In a large serving bowl, toss potatoes with chickpeas, oranges, scallions, and dressing.
