Discard soaking water and rinse the soaked kidney beans. Add 4 cups water and ½ tsp salt and pressure cook on medium heat until the first whistle. Then reduce heat and cook for 15 minutes. Blend the tomatoes and ginger to a paste. Dry roast the cumin powder on medium heat. Reduce heat and add turmeric powder, coriander powder, red chilli powder and asafoetida and roast for 1 minute (taking care that the mixture does not burn). Add the tomato-ginger paste and remaining salt and cook for 10 minutes. Mash well 1 ladleful of cooked kidney beans to thicken the gravy. Now add this to the cooked tomato paste and mix well. Add remaining cooked kidney beans and mix well. Cook uncovered on low heat for 20 minutes. Turn the heat off and garnish with coriander leaves and garam masala.