Combine the flat bread ingredients in a medium-sized bowl, then shape into a ball.
Separate into two equal portions. Using a rolling pin and your hands, flatten each portion into a circle.
Prep the red onion, apple and tuna.
In a large bowl, combine all ingredients.
Check the seasoning of your filling and adjust according to your preferences.
Heat oil in a fry pan over medium heat.
Fry the bread for 2-3 minutes, brushing oil on the exposed side. Flip, then fry the other side for 2-3 minutes.
Remove from pan, and carefully run the knife around the edge, slowly working your way towards the centre until you end up with two halves.
Sandwich the filling between the two rounds of bread.
Return to the frying pan and cook for another 2 minutes on each side.
Remove from the pan, cut into wedges and serve straight away.