Heat oil in a large frying pan. Add onion, ginger garlic paste, chillies, ground coriander and garam masala, and fry until onions turn golden brown. Add chicken pieces, turmeric, nutmeg and chilli powder and let cook for 5 to 6 minutes. Add salt and additional coriander powder to taste and cook until done. Garnish with coriander if desired, and serve.