1. Marinate the chicken pieces with ginger garlic paste, turmeric powder, red chilly powder and jeera powder, little mustard oil and salt. Keep aside for an hour.
2. Now heat mustard oil in a kadhai, add the the potatoes (cut into halves), fry them and keep them aside.
3. Now in the same oil, add chopped onions and saute till brown, add the chicken pieces and stir. put a lid and cook on a low flame with occasional stirring. Then add the potatoes when the chicken is half done, cook again till the chicken is almost done.
4. Add the tomatoes and cook till the tomatoes are mushy. Add water and bring it upto boil till desired amount of gravy is acquired.
5. Sprinkle garam masala powder and check for salt. Serve.