Wash 500 grams of bitter gourd (karela) thoroughly and pat dry. Slice them into thin round pieces and remove the seeds.
In a large mixing bowl, add the sliced karela, 2 tablespoons of salt, and mix well. Set aside for 2-3 hours to release the bitterness.
After 2-3 hours, rinse the karela slices under running water to remove the excess salt. Squeeze out the water and spread them on a clean cloth to dry for 30 minutes.
In a pan, heat 250 ml of mustard oil until it reaches its smoking point. Turn off the heat and let it cool down to room temperature.
In a separate bowl, mix 50 grams of coarsely ground mustard seeds, 25 grams of coarsely ground fenugreek seeds, 25 grams of fennel seeds, 2 tablespoons of red chili powder, 1 tablespoon of turmeric powder, and 1 tablespoon of asafoetida (hing).
Add the cooled mustard oil to the spice mixture and mix well to form a paste.
Add the dried karela slices to the spice paste and mix well, ensuring that each slice is coated with the paste.
Transfer the karela pickle to a clean, sterilized glass jar and cover it with a tight-fitting lid. Store the jar in a cool, dark place for 7-10 days to allow the flavors to develop.
After 7-10 days, the karela pickle is ready to be served. Refrigerate the jar after opening to extend its shelf life.