If jars don't seal store relish in the refrigerator otherwise they can be stored in the pantry until opened.
Replace courgettes with marrow if wished.
Salting the vegetables for a few hours helps remove any of the bitterness that the courgettes may have.
If necessary add a little extra cornflour if relish consistency is too thin, although it will thicken on cooling.
A food processor with grater attachment is a good way to grate the courgettes. Capsicum can also be chopped in the food processor if wished.