Start by boiling the overnight soaked kala chana in a pressure cooker, until it's soft enough to smash between fingers and yet retails shape.
In a heavy bottom skillet at medium heat, add the oil and scatter the whole spices. Then add ginger, garlic and green chili. Cook for 1 minute.
Add the chopped onion, season with salt and add all the ground spices. Stir it around and cook for 3 minutes.
Add the chopped tomato and continue cooking until the raw smell of the spices are gone, and you see oil releasing from the side of the pan. If at any point you feel it's sticking to the pan, drizzle a little water and continue sautéing.
Next, add the diced potatoes and the boiled kala chana. Stir it around, add ¼ cup water and cover the pan. Let it simmer for 5 minutes at medium low heat. After 5 minutes, the potatoes and kala chana should have shortened a lot more and the flavor would have blended well.
Taste for salt and add more if needed.
Add the garam masala powder and stir it around. Let it cook for 3 minutes. Finally, garnish with cilantro leaves and enjoy warm with paratha or rice.