Start by using a non-stick heavy pan/pot, add the oil, curry leaves, mustard seeds, ginger/garlic, turmeric powder, onions, tomato, chilli flakes and give it a good mix.
I always let it cook a few more minutes since I like my onions well done then I finally add the tuna fish along with the salt and black pepper powder.
Next, reduce the heat to very low and simmer for 2 minutes then remove from the stove.