In a large bowl, add the ground or chopped chicken, ginger garlic paste, green chilies, and all the spices [black salt, turmeric powder, red chili powder, coriander powder, and garam masala or chicken masala].
Mix well until you obtain a uniform mixture.
In a frying pan, add oil, and heat up on medium heat.
Once warm, add the spiced chicken mince and, breaking it down with a plastic or wooden ladle, cook it until it is done.
Once the chicken is cooked and the spices separate from the oil, remove the pan from the heat and allow the delicious mixture to cool down.
Once the chicken filling has cooled down a bit, add onion and thinly chopped cilantro [fresh coriander], and mix well.
Add salt to taste and the filling is ready.