Combine first 4 ingredients well to create marinade/dressing.
Coat shirmp and onions (separately!) with sauce and let chill 1 hour.
Spray corn with cooking oil and grill over MH heat 20 minutes, or until well charred.
Skewer onions and grill 10 minutes.
Skewer shrimp and grill until done (about 5 minutes), flipping once.
Cut corn from cob. Toss corn with all ingredients and top with dressing.