Layer the tomatoes and onions in a large earthenware bowl, sprinkling each layer with salt. Let them stand overnight. Drain off the liquid, and put the tomatoes and onions in a preserving pan. Add the green peppers, sugar, spices and vinegar. The vinegar should barely cover the vegetables, so add more or less as necessary. Simmer for 2 hours. Pour the mixture in to the earthenware bowl and allow to stand overnight.
The next day simmer the chutney for about half an hour or until there is just enough thickish liquid to cover the vegetables when they are packed together. Ladle the chutney in to heated clean, dry jars. Keep for at least 3 weeks before opening.