Heat grill to medium-high.
Meanwhile, place potatoes, shallots, oil, salt and pepper in a large bowl; toss to coat. Place two 24-inch-long pieces of foil on the counter and lightly coat with nonstick cooking spray. Arrange potatoes and shallots in a single layer, slightly overlapping, on half of each piece of foil. Leave a 2-inch border on all sides. Fold foil over and pinch the edges together, making two packets.
Place packets on the grill. Cover the grill and cook for 12 to 15 minutes, or until potatoes are tender. (When you open a packet to check doneness, be careful of steam.) Serve immediately.