I don't know if this is what Americans would term a relish - it's a British pickle called picalilli... made with strong English mustard powder as one of the ingredients, to add some 'fire'!
450g/1lb each pickling onions, peeled, cauliflower florets and de-seeded cucumber and topped and tailed French beans
340g/12oz coarse rock salt
750ml/1¼ pint white malt vinegar
1 tbsp each dried English mustard, ground ginger and ground turmeric
1 tbsp whole yellow mustard seeds
2 cloves garlic, chopped
175g/6oz light muscovado sugar
2-3 tbsp cornflour
You will need warm large sterilised jam jars with screw tops - prepare jars by washing in hot soapy water and leaving to dry and warm in a cool oven - 130C/250F/Gas ½ for 10-15 minutes.
Put the vegetables into a non-metallic bowl. Sprinkle the salt over the top, toss together, cover and leave in a cool place for 12 hours.
The next day put the vinegar into a large saucepan or preserving pan, add the spices and bring to the boil.
Drain the vegetables and add to the simmering vinegar, cook over a low heat for 20-25 minutes or until the vegetables are tender. Add the sugar and continue to simmer for a further 1-2 minutes.
Mix 2 tbsp of cornflour with a little water and blend into the hot vegetables. Bring back to the boil and cook for a further minute, the mixture should be glossy and thick. Add the remaining cornflour in the same way if necessary.
Remove the piccalilli from the heat and leave to cool for 15 minutes. Spoon into the hot jars and cover with a disc of wax paper and a screw top lid, wipe the jars and label. Store in a cool dark place for 3-4 weeks before eating.