Flip the canned tuna dipped in water and drain the water completely by pressing it with a spoon into the strainer.

In a bowl, shift the drained tuna and add mayonnaise, mustard paste, cucumber and diced onion.

Add salt, black pepper and lemon juice and mix it well.

Add coriander and again mix it well to make a sandwich mixture.

Take two slices of bread for each sandwich.

Spread 1 tbsp of softened butter on one side of a single bread slice.

Repeat the same process for another slice of bread.

Pour the tuna fish mixture on the butter side of the bread slice and make a sandwich with another bread slice.

Cut the sandwich diagonally and serve it immediately.