A buttermilk based curry which can be served with rice. It is spiced up with ginger, green chillies and seasonings.
You can also make this curry using ladies finger or ash gourd (white pumpkin), taro roots (arbi or seppankilangu) or chow-chow. I have prepared using watermelon rinds.

Boil the watermelon rind pieces in water 
Add the ground mixture to it. 

Ingredients:
For Seasoning:
Mustard Seeds – 3/4 tsp
Udad dal – 1/2 tsp
Turmeric powder – 1/4 tsp
Cumin seeds/Jeera – 1/2 tsp
Asafoetida – a generous pinch
Whole Red chillies – 2
Curry leaves – 1 sprig
Fenugreek seeds – 1/4 tsp
Chana dal /bengal gram dal – 1/4 tsp
Oil – 3/4 tsp
Other ingredients:
Thick Curds – 1 1/2 cup
Watermelon Rind cubed (without the green outer portion) – 2 cups
Water – 1/2 cup
For grinding:
Ginger – less than 1/2 inch piece
Green chillie – 2 or 3
Tur dal – 1 1/2 tsp
Raw Rice – 1/2 tsp
Coriander seeds – 1 tsp
Jeera – 1/2 tsp
Coconut grated- 1/2 cup
Preparation:
Grind all the ingredients listed under ‘grinding’ to a fine paste in a mixer. You can add 2 to 3 tbsps of water while grinding.
Chop the watermelon rinds into bite size pieces and boil them in 1 cup of water with salt and turmeric powder. After it is cooked, keep them aside. Do not throw away the water left after boiling the watermelon rinds. It can be addded to the curry.
Add the ground coconut mixture to the cooked watermelon. Add 1 cup of water and and boil it for 6-7 minutes on low flame until the raw smell disappears. Put off the flame and keep the curry aside. When it cools down and is warm, add the thick curds to it and stir gently. You can keep it on fire and heat it gently on low fire for 1 minute making sure that the curds does not curdle.
Place a seasoning and heat it. Add oil and add the ingredients “under seasoning”. Pour the seasoning on top of the more kolambu or buttermilk curry. Mix and serve with rice.