First of all, in a big pan, blanch/par-boil jackfruit pieces with 1/2 teaspoon of salt in enough water. Please ensure that Jackfruit should be left tender only and not fully cooked.

Drain the water completely and spread them on a towel in the sun or under the fan for 1 hour. The idea is to let the moisture evaporate fully.

Now, dry roast the fennel and cumin seeds for 4-5 minutes and grind them coarsely.

In a pan/kadhai, heat half of mustard oil to its smoking point. Switch off the heat and let the oil cool for 3-4 minutes. Add jackfruit pieces and all the spices and vinegar and mix well. Transfer this to a glass jar in which you are planning to store your pickle.

Now, heat rest of the oil for 3-4 minutes and pour it into the pickle filled jar. Close the lid and give the jar a good shake. Keep it in sunlight for 3-4days and it would be ready to eat.