Wash the tomatoes, remove the stem, cut in half lengthways and cut out the green and white stem. Halve each half lengthways, remove the grains and cut the quarters into thirds crosswise. Roughly cut a peeled half onion into rings. Quarter larger rings.
Wash the fresh celery, shake dry and pluck and chop the flawless leaves. Use two tablespoons of it immediately and freeze the remaining leaves. Take 2 tbsp of the frozen goods and let them thaw. Cut the flawless stems crosswise into approx. 3 mm wide rolls and freeze in portions.
Cut the tuna into smaller pieces and place in a bowl with the oil. Add all remaining ingredients except for the feta and mix well. Season with salt and pepper, fresh from the mill.
Arrange the salad on 2 serving bowls, spread the feta over the top, garnish, serve with toasted white bread and enjoy.