1 tin of tuna, well drained (I like Clover Leaf Skip Jack Flaked Tuna in water)
2 tbsp mayonnaise
1 tbsp onion, minced
1 tbsp coriander, minced
1 green chilli, seeded and minced (if the chilli is really small I don't bother to seed it)
salt and freshly ground pepper to taste
Mix all above ingredients together.
Now make a sandwich!