- Combine mustard seeds and vinegar in a small bowl and stand overnight. Combine coconut, water and extra vinegar and stand for one hour.
- Heat oil in a large pan and cook onion, garlic, ginger, chili, all powders until fragrant. Add tomatoes and cook until soft.
- Stir in mustard mixture and bananas, simmering uncovered until thickened.
- Stir in sugar, then coconut mixture. Simmer uncovered, stirring occasionally for about 10 mins, or until thickened. Stir in remaining ingredients.
- Spoon the hot relish into sterilised jars and seal.