Place the yogurt, coriander leaves, mint leaves and chillies into a hand blender or a regular blender and blend until smooth. Set aside.
Heat oil in a large pot or skillet, and add the chicken. Saute for 4-5 minutes or until the chicken changes color.
Add the ginger garlic paste and cook for a 3-4 minutes until fragrant.
Now add the green yogurt masala and 1-2 tablespoons of water. Lower the heat and cover the pot with a lid.
Cook for 5-7 minutes, while stirring in between, until the chicken is cooked through.
Remove the lid, and increase the heat.
Cook the hariyali chicken on high heat, while stirring continuously, until you see the oil separating from the curry and the gravy has thickened slightly.
Add lemon juice and butter, and mix.
Serve with rice, paratha or naan.