Firstly wash the kidney beans very well and soak them overnight or for 6 - 8 hours.
In the morning or after they have soaked, rinse them well. Pressure cook the kidney beans with enough water and salt.
Now make a fine paste of fried onions, tomato, ginger and garlic. Once the paste is done heat a teaspoon of oil and saute the paste. Add red chilly powder, turmeric powder,coriander powder and gram masala. Cook the spices with the masala till oil separates.
Now mix this spice paste to the cooked beans. Add water to adjust the consistency of the gravy. We do not want a very thick gravy.
Pressure cook for one more whistle. Open the cooker after the pressure is released.
Now take a bun, cut it into pieces. Place in a serving bowl. Pour a ladle full of the prepared Rajma over the bun, soaking them well.
Drizzle chutney, sprinkle chaat masala, red chilly powder. Garnish with onion slices and green chillies.