Heat 1 tbsp gingelly oil in a pan. Add the lemons and stir until their skin becomes soft, turning them on all sides. It takes about 5 – 8 minutes. (Alternatively, you can steam the lemons for 8 – 10 minutes until they turn soft). Cool them completely. Cut into 8 pieces. Transfer into a glass jar or a bowl. Add enough salt and 1.5 tsp sugar to the lemon pieces. Mix well and set aside for 1 – 2 days or a minimum of 2 hours.
Heat 2 tbsp gingelly oil in a deep pan. Splutter mustard seeds and fry dry red chilies. Add sliced ginger, garlic and green chilies. Fry until lightly golden. Next add chopped dates. Cook until soft, about 3 minutes. (Add 1 more tbsp gingelly oil, if required). Bring down the heat to low. Add chilly powder, fenugreek powder, hing and 1 tsp sugar. Saute for a minute. Next add hot water, salt and vinegar. Boil for 2 minutes until thick. Switch off. Set aside to cool. Add the lemon pieces. Combine well. Check for salt. Cool down and transfer to an airtight jar.
Heat 1 tbsp oil in a small pan. Cool completely. Pour the cooled oil on top of the pickle. You can have it after 2 – 3 days but it tastes best after 2 – 3 months. Keep refrigerated in order to increase its shelf-life.