Broil or grill the jalapeños until the skin starts to blister and they start to get soft. Let cool. Peel off the skin that comes off easily. Seed and coarsely chop them.
Roast the onion in a dry pan, stirring constantly until brown and soft. Chop up all the rest of the ingredients to the texture you like, and mix them together in a bowl. Keeps refrigerated for three days or so.