Drain and prepare Drain the tuna thoroughly and break it into small flakes. Rinse and drain the beans, measure half the drained can and refrigerate the remainder. Chop the celery and parsley. Shred and dry the lettuce. Keep the ingredients in separate small piles so you can see whether any still carry excess water.

Make a coarse bean base Put about one-third of the measured beans in the mixing bowl. Mash with a fork until they form a rough paste with only a few small lumps. Stir in the olive oil, lemon juice and black pepper. The paste should loosen enough to coat other ingredients without becoming a pourable dressing.

Fold rather than beat Add the remaining whole beans, tuna, celery and parsley. Turn the mixture over gently with a spoon until the dressing is distributed. Leave visible tuna flakes and whole beans. Scraping and beating repeatedly will turn the filling into a uniform mash and lose the texture this recipe is built around.

Check the consistency and seasoning Lift a spoonful. It should sit in a soft mound, with no liquid running off the spoon. Taste before adding salt; tuna and canned beans vary in saltiness. If the mixture is crumbly, mash a few more beans into it before considering the small dressing adjustments described below.

Open the pockets Cut each pita round in half across its diameter, giving four halves. Gently separate the inside walls with your fingers. Use the bread at room temperature if it bends easily. If stiff, warm according to its package instructions just until pliable, then let trapped steam escape before adding the cold filling.

Fill lightly and serve Divide the lettuce among the four pockets. Divide the tuna mixture into four portions and spoon it in gently, stopping before the bread is stretched tight. Leave a little space at the opening. If a pocket is smaller than expected, serve its extra filling alongside instead of forcing it inside. Serve two halves per person.