Heat the oil and fry the finely chopped onions, garlic and ginger.
Add the spices and cook for a few minutes longer.
Add the tomatoes and salt to taste and cook for a further 5 minutes.
Put in the chicken pieces and stir so that they are thoroughly coated with the gravy.
Cover the vessel and simmer for about 30 minutes at the end of which, the mixture should be almost dry. But you need to check from time to time and add a little water if necessary.