WHISK first 4 ingredients until well blended. Pour 1/4 cup over steak in shallow dish; turn to coat both sides of steak. Refrigerate 20 min. to marinate, turning occasionally.
MEANWHILE, heat grill 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 center of large sheet heavy-duty foil. Bring up foil sides. Double fold top and ends to seal packet, leaving room for heat circulation inside.
REMOVE steak from marinade; discard marinade. Grill steak and foil packet 10 min. or until potatoes are tender and steak is medium doneness (160ºF), turning steak after 5 min. Remove both from grill. Cover steak; let stand 5 min. Meanwhile, cook beans.
CUT steak diagonally across the grain into thin slices. Serve with potatoes and beans.