Peel pumpkin and cut into large pieces.
Put all ingredients into a medium saucepan except the 1/2 cup of coconut milk and the mustard seeds. Place on a medium heat and slowly bring to a simmering heat. Cook uncovered until pumpkin is almost soft. Grind mustard seeds in a suribachi and add to the 1/2 cup of coconut milk. Add this to the pumpkin and cook for a further 5 minutes on a low heat. Serve with lentil rice.