To begin, empty out tuna chunks in a bowl.
Heat mustard oil in a pan to the smoking point and let it cool a bit.
Add in finely chopped onions and saute until translucent. Next, add in the ginger garlic paste and saute for a minute or two.
Now add in the dry masalas - salt to taste, Kashmiri red chilli powder, cumin powder (jeera), and coriander powder (dhania). Mix well.
Add in the vinegar and mix.
Now add the tuna chunks and fold them in gently. Cook until the oil starts appearing on the sides.
Finish with garam masala powder and mix well. Adjust the salt and more if required.
Although it is ready to eat, let the pickle stand for about an hour so that the tuna pieces absorb the masala. Enjoy with paranthas or use it as a relish.