Wash your cilantro and peel and roughly chop your ginger. Now grab a blender and toss in the cilantro, green chillies, chopped ginger, garlic, yogurt, salt, cumin powder, coriander powder and ¼ cup of water. Puree till smooth
Put a wok or large bottomed pan (quicker to cook than in a small one) on medium heat and add in a few tbsp of oil.
While that's heating dice your onions and add saute till the onion becomes translucent.
Add the chicken, sprinkle with red chilli powder and salt and stir fry till the raw look of the chicken is gone.
Now add the green paste, stir to coat the chicken, drop the heat and let it gently simmer (covered) for 15-20 minutes at which point your chicken should be cooked through and the oil should have risen over the masala.
Check for seasoning, garnish with some fresh ginger or fresh chillies. Serve with roti or rice.