Place all the ingredients in a medium-size pot. Bring to a boil over medium-high heat, then turn down the heat to medium-low. Allow to simmer, uncovered and without stirring, for about ten minutes until the sugar has melted and the mixture has reduced by at least one third.
Transfer to a food processor and pulse the mixture briefly, five or six times. This will ensure the relish has texture.
Transfer to a container and allow to cool to room temperature, uncovered. One cool, seal the container and place in the fridge to sit for at least two hours before serving.
Keep in an airtight container in the fridge for up to two weeks.