Heat oil in a kadai/non-stick pan.
Open the tuna can and drain the liquid.
Add mustard after it splatters add curry leaves, cumin seeds, shallots, green chili and ginger.
Add a little salt and stir until shallots are soft and comes translucent.
Add turmeric powder, coriander powder, chili powder and a splash of water, mix well and simmer for 2minutes.
Now add the tuna, break it down as you stir.
Add more salt if needed. See notes.
Add 1/4 th cup of water and close with a lid for 5 mins.
Add grated coconut and fresh coriander leaves and cook for a minute. Turn of the stove.
Serve with rice and hot rasam.