Grind onions and peppers together, coarsely, in food processor or food chopper. Mix well, including juice. Cover with boiling water and rest for 5 min. Drain off water; squeeze dry.
Add vinegar, salt and sugar; bring to a boil and cook for 20 min.
Put in clean jars and cover tops with olive oil; refrigerate. To put up in jars, double all quantities (leave out the olive oil) and seal in sterile jars.