Heat sufficient water in a deep non-stick pan, add drumsticks, salt and ¼ tsp turmeric powder and cook till the drumsticks are soft.
Heat oil in another non-stick pan. Slice onions.
Add mustard seeds to the oil and let them splutter.
Slit green chillies.
Add curry leaves to the oil and sauté for ½ minute. Add onions and sauté till the onions turn soft.
Put 4 tbsps scraped coconut in a grinder jar, add 3-4 tbsps water and grind into a smooth paste.
Add ¼ cup water to the onions and cook for 2 minutes. Add crabsticks, coconut paste and salt and mix well.
Add green chillies, mix well and cook for 3-4 minutes. Add cooked drumsticks along with the liquid, kokum petals and remaining turmeric powder and mix well.
Add remaining scraped coconut and mix well. Cook for 2 minutes.
Transfer into a serving bowl and serve hot.