Rinse beans cold and drain well. Onions peel, halve and cut into strips. Clean, wash and chop the tomatoes. Wash herbs and shake dry. Pluck thyme, cut chives into fine rolls.
For the marinade, peel the garlic and chop very finely. Mix well with vinegar, 1 level tsp salt, 1⁄2 tsp pepper and sugar. Fold in the oil. Mix with the prepared ingredients and season to taste with some Tabasco.
Drain tuna well. Finely puree with salad cream and sour cream. Season to taste with salt and pepper. Arrange bean salad with tuna cream.