Clean, peel and cut the onion into fine cubes. Wash, core and cut the peppers into small cubes. Dice the cheese as well. Cut the olives into rings and mix the prepared ingredients with the walnuts.
Make a salad dressing from vinegar, oil and mustard and season with salt and pepper. Mix the dressing with the ingredients and let it steep. Garnish the salad with a little parsley before serving.
The salad can also be prepared the evening before and filled into glasses. It is a very good salad-to-go for those who are hungry during the lunch break.