Peel and roughly chop the plantains into about 2 inch pieces. Cook the plantain cubes with about 1/2 cup water till it is cooked (soft but still intact). Add the crushed jaggery to this and cook till the jaggery has melted. Add turmeric and salt to this.
Grind the coconut and red chillies with a little water to a smooth paste. Add this to the plantain – jaggery mixture. Mix well and let it cook for a couple of minutes.
Heat the oil in a small pan and add the mustard seeds to it. Once the mustard seeds have spluttered, add the curry leaves and pour this over the pachadi.