Wash, clean and slice the tomato. Leek clean, wash and cut into thin rings. Drain the celery. Peel garlic and press it through a garlic press.
Mix celery with garlic and yoghurt, season with pepper. Drain the tuna, pluck it into small pieces. Cut the bread roll in half horizontally once. Spread tomato slices on the lower half of the roll.
Season with salt. Spread the celery salad, tuna and leek on top. Garnish with marjoram. Put the lid of the bread roll on top and serve.