These skewers can be prepared on the outdoor grill or under broiler. If cooking on the grill, preheat to medium-high.
Heat the broiler to high. Place the peppers on a baking sheet and char them all over, about 15 minutes. Leave the door cracked a bit so steam can escape.
While peppers roast and blacken, bring a couple of inches of water to boil in a skillet. Add sausages and par-cook them by boiling them for 5 minutes.
While the sausages cook, bring a medium-size pot of water to a boil. Add onions and cook 5 minutes. Drain them then wipe off the skins and trim off ends with paring knife.