Soak pigeon pea in water for 30 minutes; drain and keep it aside.
In a pressure cooker add avarakkai, soaked pigeon pea. Add 1/4 cup of water and cook for 3 whistle and release pressure. NOTE: you can cook in pan. then you have cook (steam or boil) avarakkai with as little water as possible. You have to cook the pigeon pea separately until its easy to be mashed.
Heat oil in a pan; add mustard seed, split black gram. Wait until the mustard seed stop to splatter.
Now add the chopped onion and cook until it turns golden brown.
Now add the cooked Avarakkai sauté and cook until excess water is gone.
Now add salt to taste, chili powder. Simmer and cook for 2 to 3 minutes. Time to time mix it and make sure it done not get burnt.
Finally add the cooked pigeon pea, coconut and cook until coconut raw smell is gone.