1Brush grill rack with vegetable oil. Heat coals or gas grill for direct heat.
2Husk corn and remove silk. Brush corn and onions with oil.
3Cover and grill corn and onions 4 to 6 inches from medium-hot heat 5 minutes. Remove onions from grill; set aside. Turn corn. Cover and grill about 15 minutes longer, turning twice, until tender. Remove corn from grill; cool 20 minutes.
4Cut corn from ears. Cut onions into slices. Mix corn, onions and remaining ingredients.