Tuna is a staple of Tunisian street food, so you'll find a variety of different types of tuna sandwiches.

If you are looking for a standard Tunisian sandwich, I asked my wife and she said this one looks good: https://www.saveur.com/article/Recipes/Tunisian-Tuna-Sandwic....

Fricassee is another tasty Tunisian tuna-based sandwich, but it requires that you also prepare the bread: http://www.afooda.com/tunisian-fricassee-fricasse-roll/