Heat 2 tablespoon oil in a pan, saute lime until the color changes. It takes about 5 - 10 minutes. Allow it to cool and cut each lime into 8 pieces. Discard juice and oil.
Heat 1/2 cup oil in a pan, fry mustard seed, fenugreek seed, garlic, ginger and green chilli slightly. Remove pan from heat and add kashmiri chilli powder, chilli powder, turmeric powder and asafoetida powder.
Add chopped dates along with little boiling water and cook in low flame until soft. Add required amount of boiling water, salt, vinegar and sugar, bring to boil until thick. Switch off flame and add lime pieces, mix well and adjust the taste.
Let it cool completely and store in airtight container. Pour little oil on top of the pickle. Keep refrigerated to increase the shelf-life.