Clean the beans, wash them, possibly cut them smaller. Cook in boiling salted water for about 15 minutes, drain. Meanwhile clean and wash the peppers and radishes. Cut the bell peppers into pieces and the radishes into fine slices.
Wash sugar snap peas, cut in half lengthwise, cook in salted water for 3 minutes, drain. Peel onions, cut into rings. Rinse beans and drain. Bring stock and vinegar to the boil briefly.
Pour hot over prepared salad ingredients and mix. Clean and wash the lettuce leaves and pluck into small pieces. Line plates with them. Arrange salad on top. Cut trout fillet into pieces and spread on the salad.