Pressure cook the potato and black soaked chana for 4-5 whistles. Open the cooker and evaporate the water completely and keep aside.
Heat oil in a pan. Add the chopped onion ,ginger garlic paste, chillies and fry till onion turns soft.
Add chopped tomatoes and fry till it becomes mushy. Add the turmeric powder, chilly powder, season with salt and fry for a min.
Add the cooked potato and black chana and stir well. Cover the pan and fry on low-medium heat for about 10 mins stirring it occasionally.
Add garam masala powder and increase the heat and fry on high heat for 5-10 mins till the potato is roasted well and starts to crisp. Take off the flame and serve as a snacks or side dish.