Drain the tuna and pick apart with a fork. Rinse the lettuce, pat dry and tear into bite size pieces.
Rinse the tomatoes, quarter, remove the seeds and cut into small cubes. Rinse and finely chop the celery. Finely chop the celery leaves.
Mix the creme fraiche and lemon juice. Peel the garlic and press into the creme fraiche mixture. Mix in the tuna, tomatoes, lettuce, celery cubes and celery leaves. Season with salt and pepper.
Spread the tuna and vegetable mixture over four slices of bread. Place the remaining slices of bread on top. Cut diagonally and serve.