Clean, wash and drain the beans. Cut diagonally into pieces and cook in boiling salted water for 8-10 minutes. Clean, wash and thinly slice the tomatoes. Peel onion and cut into wafer-thin strips. Finely dice the bacon and fry it crisply in a pan without fat. Add onion, oil and vinegar to the bacon and mix. Season with salt, pepper and sugar
Drain the beans and quench them briefly in cold water. Arrange beans with tomatoes on plates, drizzle onion-bacon vinaigrette over them. Slice the cheese thinly with a peeler and sprinkle over the salad. Serve lukewarm, garnish with chives as desired