Mix the mayonnaise and natural yoghurt together in a bowl, then add the carrot and raisins
Remove tuna from the can and flake with a fork to break up the chunks. (Mix with a teaspoon of low-fat mayonnaise and a teaspoon of low-fat natural yoghurt if desired.)
Place tortilla on plate.
Place 1/4 of the lettuce, tomato, carrot mixture and tuna in the centre of the tortilla. Fold up the bottom of the tortilla then roll. Voila!