Boil potatoes in a pot of water with little salt till soft for about 20 minutes.
In a bowl, mash hot potatoes with a fork and combine with the tuna flakes, mayonnaise, flour and breadcrumb. Add egg, mix well and blend in coriander leaves with a dash of salt and pepper. Refrigerate tuna mixture for 30 minutes. (you may add a little more plain flour if mixture is too soft).
Grease spoon with some oil, so the tuna mixture will slip into the hot oil easily. Deep fry tuna balls at medium low heat till golden brown.
Place tuna balls on a kitchen paper to drain away oil before serving.