Quarter and deseed the peppers, then place, skin-side up, on a grill pan. Grill until the skins are blackened, then transfer to a bowl and cover with foil until they are cool enough to handle. Strip off the skins and roughly chop the peppers.
Roughly chop the tomatoes and garlic. Deseed and roughly chop the chilli. Put all the ingredients in a food processor with a good amount of seasoning. Blitz until finely chopped but not puréed. Tip into a bowl, cover and chill for up to 3 days. Bring to room temperature to serve.