Place the potatoes in a pot of water and boil
Once potatoes are boiled, take them out and mash them using a fork and leave aside ( it does not have to be thoroughly mashed)
Heat a pan with oil on a medium fire add onion, garlic, ginger, chilli, curry leaves and mustard seeds and cook until soft
Add in the potatoes, tuna, curry powder, turmeric, chilli powder, cumin, salt, pepper and cook for 1 minute
Take the pan off the fire and add the lemon juice