Mix the rajma dal and black gram and soak in water for 5-6 hours. To this add Bengal gram and pressure cook for 30 minutes.
Heat oil in a pan, fry the onions and ginger-garlic paste for few minutes. Then add coriander powder, chili powder, turmeric and fry for another 2-3 minutes.
To this, add tomatoes and cook until they are mushy.
When thick gravy forms, add boiled dal and cook with salt and water if required for 10-15 minutes.
Now add garam masala and stir well. Remove from heat and serve with rice or chapathis