Using a sharp knife, make 3-4 deep slits on each of the chicken drumsticks.
Marinate the chicken with ginger paste, garlic paste, green chili paste, coriander leaves paste, ½ tbsp lemon juice, 1 tbsp mustard oil and a little salt, keep aside for at least 3-4 hours. (The longer the merrier !!)
Heat the remaining oil in a thick bottomed pan, when smoking hot, throw in the sliced onions, fry till golden brown.
Add the marinated chicken along with the marinade and the slit green chilies. Cook over a low flame till oil starts to separate from the masala.
Add 1/2 a cup of warm water, throw in the whole green chilies, give it a hearty stir.
Adjust seasonings, continue to cook till the chicken is tender and the gravy is of a coating consistency.
Finish with the remaining lemon juice and chopped coriander leaves. Serve hot with rice or parathas.