1.Combine mustard seeds and vinegar in small bowl, cover; stand overnight. Combine coconut with the water and extra vinegar in medium bowl, cover; stand for 1 hour.
2.Heat oil in large heavy-base saucepan; cook onion, garlic, ginger, chilli, chilli powder, cumin and turmeric, stirring, until fragrant. Add tomato; cook, stirring, until tomato is soft. Stir in mustard seed mixture and bananas; simmer, uncovered, stirring occasionally, until mixture thickens.
3.Stir in sugar, then coconut mixture; simmer, uncovered, stirring occasionally, about 10 minutes or until mixture thickens. Stir in remaining ingredients. Spoon hot relish into hot sterilised jars; seal while hot.