Strain the tuna and tip it into a bowl. Add 4 tablespoonfuls of mayonnaise and ½ tablespoonful of wholegrain mustard, a few drops of lemon juice and a spoonful of Modena balsamic glaze. Stir well. You can adjust the quantities up or down, but make sure the tuna isn’t swamped in sauce.
Chop up the celery and walnuts (in small or large chunks) and add to the mixture.
Once the mixture is ready, you can fill the wraps. Spread some fresh spinach on the inner third of the wrap and spoon some of the mixture on top, followed by another layer of spinach. Fold in both sides of the wrap and roll it up. Cut each wrap in half diagonally before serving.