Place chiles on grill 4 to 6 inches over hot coals. Cook until chiles
are blistered and somewhat charred on one side. Remove and peel
any skin that removes easily. Slit lengthwise down the cooked side
and remove seeds.
Mix shrimp and onions and fill chiles with mixture. Place over medium
fire and cover grill with lid. Cook without turning until shrimp
mixture is hot to touch (5-7 minutes).