Take a bowl of water with little salt and curd or buttermilk. Cut banana stem like round disc and remove the fiber by using the finger. Cut the disc into small pieces and add in the buttermilk water mixture. It helps to prevent from oxidation aand maintain it's original colour.
Boil plantain stem with the same water mixture by adding little turmeric powder. Let it boil for few minutes. Strain water and keep it aside.
Heat oil in a wok on medium flame. Add mustard seed, urad dhal and bengal gram and cummin seed. Let it splutter. Add chopped onion and garlic and saute well. Add green chillies to it. Add boiled plantain stem and mix well. Add pressure cooked thoor dhal to the mixture and saute.
Add salt to taste and cummin powder. Let it saute for a minute minute. Add shredded coconut, curry leaves and coriander leaves. Healthy Plantain stem kootu is ready to have with sambhar, rasam and curd rice. It can have like a salad too.