Soak the dry flat green bean seeds (sheem bichi) overnight . Drain from water. One seed at a time, gently press the seed with your thumb. The fine seed membrane shall peel off easily. Remove for all the seeds.
Pressure cook the seeds in salt water, 1 whistle or so.
Smear the koi maach with just a pinch of turmeric and salt.
Heat 4 tbsp oil in a kadhai, shallow fry the koi maach. Keep aside.
In the same pan, fry the potatoes, keep aside.
Add the remaining mustard oil into the same pan, throw in the cumin seeds, bay leaves and dry red chillies. Allow the spices to splutter.
Stir in the ground masala paste, ginger paste and the remaining turmeric powder. Continue to stir fry over a medium flame until the masala starts to release oil.
Pour 2 cups of warm water, throw in the potatoes, chillies and boiled flat green bean seeds. Gently place the fried koi maach in the curry. Cover and cook over a medium flame for 7-10 minutes. Serve hot.