Start by Washing the dal. Now Soak toor dal for 1 to 2 hours. Drain them and set aside.
Take beans and salt in a saucepan and cover it with water. Bring it to boil and cook it for 10 mins till the beans is cooked. Drain it and set aside.
Take dry red chilli, salt, asafoetida, turmeric in a blender and blend them first. Once they are blended add in toor dal and make them to a coarse puree.
Heat oil in a kadai. Add in mustard and urad dal and let it sizzle.
Now add in the pureed dal mixture and keep frying till it becomes crumbles and gets cooked. It will take around 10 mins.
Now add in the cooked beans and mix well with the dal. Taste and adjust the seasoning.
Stir fry this for 5 to 8 mins till everything is combined.
Serve hot with rice and any spicy gravy like pulikulambu.