Prepare grill or broiler.
Place corn on grill rack or broiler pan; cook 20 minutes or until corn is lightly browned, turning every 5 minutes. Cool. Cut kernels from ears of corn to measure 3 cups. Place onion on grill rack coated with cooking spray; cook 5 minutes on each side. Cool and chop.
Combine corn, onion, and remaining ingredients in a large bowl; toss well.