Mix the onion, green chili, ginger, chili powder, turmeric powder, pepper powder, salt and yoghurt to make a marinade. Make 2-3 deep cuts in the chicken drumsticks. Place them in a glass dish and coat them evenly with the marinade and refrigerate for 3 hrs. Heat oil in a deep pan. Fry the marinated chicken pieces for about 12-15 minutes or until browned. Garnish with chopped coriander leaves and serve hot.