Wash the green chilies. Remove the stem and pat dry with a clean towel. If possible place them in the sunlight for 15 - 20 minutes to completely dry.
Slit the green chilies lengthwise and cut each one into 2 - 3 pieces. Set aside.
Coarsely crush the mustard seeds in a blender. Combine mustard seeds, salt, achaar ka masala, and salt. Mix nicely.
Now in a clean bowl mix green chillies, garlic cloves and the spice mix.
Toss the green chillies nicely in the spice mix. Transfer the pickle to a clean, dry jar.
Now heat mustard oil in a pan till it starts smoking. Turn off the heat.
Allow the mustard oil to cool down a bit. Pour the mustard oil over the pickle in the jar.
Seal the jar with a lid. And shake gently once.
Instant Green Chilli Pickle is ready to serve.
Store it at room temperature for a month or so.