Soak Bengal gram, split black gram in water until they are submerged in two separate bowl. Place the copped cabbage in a bowl.
Steam and cook in Idly pan all the bowl for 15 minutes or until the grams and cabbage cooked.
In mixer grind coconut, dry chili, cumin seeds, water as needed and grind to fine thick paste.
In pan add the steam cooked Bengal gram, black gram along with water. Add the steam cooked cabbage, turmeric powder as well. Cook this until they start boiling.
Now add ground coconut paste, 2 tablespoon (tbsp.) of water and cook for 5 minutes. Now add salt as needed and cook for two minutes or until they become little thick.
In pan heat oil add mustard seeds. once the stop splattering add this to koottu, mix well and remove from Heat.
If you want to thicken the koottu you can make rice paste by mixing 1 tablespoon (tbsp.) rice flour, 2 tablespoon (tbsp.) of water with no lump. add this rice and cook to the koottu before you add the mustard until the right thickness is reached.