Wash and dry the chillies.Slit them into halves or chop them into bite-sized pieces and keep aside.
In a bowl, mix the salt, turmeric powder, cayenne and crushed mustard seeds along with lemon juice.Add this to the chillies.
Heat the oil (if using mustard oil). Let it smoke and then add to the chillies-spice mix.Let it cool down completely.
Now take a sterilised glass bottle and fill the chillies with the spice mix in it.
You can keep it in the sun for 2 days or in a warm place.
You can start eating the pickle after 2 days.
It tastes quite good within a couple of days when the mustard has matured and lent a tart taste to the chillies.
Notes
1. Use the thin green chillies preferably the mild or medium spicy ones.2. You can use any vegetable oil but mustard oil adds more flavour.3. The chilly gets mellowed in taste as the pickling happens.4. Have it as a side to your parathas or meals.5. Adjust the quantity of salt as per your taste.6. You can skip the cayenne if you like.