Canning method
Wash and coarsely grate or finely chop tomatoes, peppers, and onions. Dissolve salt in water and pour over vegetables in large kettle. Heat to boiling and simmer 5 minutes. Drain in colander. Return vegetables to kettle. Add sugar, vinegar, mustard, and cornstarch. Stir to mix.
Heat to boil and simmer 5 minutes. Fill sterile pint jars with hot relish, leaving 1/2-inch headspace. For more information see "Sterilization of Empty Jars" . Adjust lids and process according to the recommendations in
Processing: Process Hot, Pints, boiling-water canner, 0 - 1,000 ft - 5 minutes.
Altitude-adjusted processing table: Table 1. Recommended process time for Pickled Green Tomato Relish in a boiling-water canner. / Process Time at Elevations of / Style of Pack - Jar Size - 0 - 1,000 ft - 1,001 - 6,000 ft - Above 6,000 ft / Hot - Pints - 5 min - 10 - 15