1. Fill a small pot with plenty of water to heat up and prepare the green beans. With a small, sharp knife, trim off the two ends and then pull downwards to remove the strings. If they are large, cut them in half. Rinse the green beans well and put them in the boiling water, adding a little salt.
2. Boil until the green beans are cooked. Take them out and place them in a bowl of water and ice cubes to cool down. This way, they will stay green. Remove them onto a plate lined with kitchen paper to drain.
3. In a large salad bowl, combine all the ingredients.
For the Dressing:
1. In a small bowl, whisk together the olive oil, vinegar, mustard, salt, and pepper.