Grind green chillies, garlic, and salt into a rough paste using a blender.
Put the paste in a bowl or jar.
Heat some oil in a small pan.
Add mustard seeds and wait for them to pop.
Add a pinch of asafoetida to the pan and then turn off the heat.
Pour the hot oil mixture over the green chilli paste and mix well.
Serve the Green Chilli Thecha with Hot Tea.