Steam the lemon. When it is half cooked, wipe out the water from it. Heat some gingelly oil and sauté the lemon in a low flame and allow to cool. Wipe out the excess oil from the lemon. Cut each lemon into 8 pieces. Mix well with 1/4cup of salt and keep aside.
Season mustard and fenugreek in 2dsp of gingelly oil. Saute the 4th ingredients and add water, vinegar and sugar into it. When it boils, remove from fire and add the lemon pieces. Mix well. Pickle is ready.