Cook 2 teaspoons of mustard seeds over a medium heat in a medium heavy-based pan for 1-2 minutes, or until they begin to pop. Add 1.5kg of peeled, seeded and chopped tomatoes, 250g seedless green grapes, 1/2 cup sugar, 1 cup red wine vinegar, 1 teaspoon garam masala and 2 chopped small red chillies. Stir to combine. Simmer for 45 minutes, or until the mixture thickens and the grapes are soft. Serve immediately or spoon into hot sterilised jars. Store in the fridge for two weeks.