Scald the tomatoes, peel them, remove the stalk and dice. Mix with the desiccated coconut. Remove the stalks and seeds from the chili peppers, finely chop, stir into the yogurt with the tomato and coconut mixture. Season with salt and pepper.
Heat the oil in a small pan, toast the mustard seeds and crushed chilli pepper in it, stir into the yoghurt. Serve well chilled.