Rinse the dried rajma under running water and soak them in 4 cups of water overnight or for at least 6-8 hours.
After soaking, drain the water and rinse the rajma again.
In a pressure cooker or a large pot, heat oil or ghee over medium heat. Add cumin seeds and let them splutter.
Add finely chopped onions and sauté until they turn golden brown.
Add ginger-garlic paste and sauté for a minute until the raw smell disappears.
Add chopped tomatoes and cook until they turn soft and mushy.
Add slit green chili (if using), turmeric powder, coriander powder, red chili powder, and salt. Mix well and cook for another 2-3 minutes.
Add the soaked and drained rajma to the pot along with 3 cups of water.
If using a pressure cooker, close the lid and cook the rajma for about 15-20 minutes or until they are soft and tender. If using a pot, cover and cook on medium heat for about 45-50 minutes or until the rajma is cooked through, stirring occasionally.
Once the rajma is cooked, add garam masala powder and mix well. Adjust salt and spices according to taste.
Garnish with freshly chopped coriander leaves and keep it aside.