Meanwhile, heat barbecue to medium-high heat. Prick potatoes in several places with fork or sharp knife; microwave on HIGH 4 min. Let stand 2 min.; cut into 1/4-inch-thick slices. Place in medium bowl. Add remaining dressing mixture; toss to coat. Place on centre of large sheet heavy-duty foil. Bring up foil sides. Double fold top and ends to seal packet, leaving room for heat circulation inside.