HEAT grill to medium heat.
GRILL corn and onions 4 to 6 min. or until lightly charred, turning after 3 min. Place in large bowl; cover with plastic wrap. Let stand 10 min. to allow vegetables to steam until tender.
CUT corn kernels from cobs; place in medium bowl. Chop onions; add to bowl with corn. Stir in remaining ingredients.
REFRIGERATE 15 min.