Clean the salmon and remove its skin and bones. Pat dry the fish using a cloth or paper towel. Cut it into bite-size pieces.
Combine the ingredients to make fried fish (ingredients from 1 - 8) together and marinate the fish for half an hour.
Into a sauce pot, pour 1 cup white vinegar and bring it to boil. Once it starts to boil, turn off the heat and set aside to cool to room temperature. (Refer Note: 1 )
Heat a frying pan on medium. Then add coconut/sesame oil, enough to fry. Once the oil is hot, fry the marinated fish pieces in small batches. Do not disturb the fish pieces for 2 minutes. Then, lightly stir the fish pieces and fry each side until it gets crispy and golden brown in color. It takes approximately 8 to 10 minutes to fry both sides. Transfer this to a bowl.
Reduce the heat to low. Fry green chilies and curry leaves in the same oil until crisp. Remove this to the bowl with fried fish.
Then fry julienne cut ginger until it becomes light brown ( do not burn ) in color and move to the bowl.
Finally, add garlic cloves and fry till crisp and golden in color. Transfer this to the bowl with fried fish and set aside. ( Refer Note: 5 )
In a small bowl combine the ingredients to make masala paste (turmeric powder, fenugreek powder, Kashmiri red chili powder, red chili powder and salt). Add water little by little to make a thick paste. ( Refer Note: 2 )
Place a heavy bottom pan on medium heat. Add sesame oil. Splutter mustard seeds and fry dried red chilies.
Add asafoetida powder and masala paste to the oil. ( Refer Note: 3 ) Fry it for a minute and add 1/4 cup water. Cook till the raw smell goes.
Reduce the heat to low and add the fried fish along with fried curry leaves, green chilies, ginger and garlic. Combine everything well.
Turn off the heat. Pour the cooled down vinegar to the fish masala and mix well. Allow the pickle to cool completely to room temperature.
Transfer the fish pickle to an air tight and cleaned jar / container. You can use this immediately. But it tastes better after a week. ( Refer Note: 4 )