In a large bowl, combine the olive oil, red wine vinegar, Dijon mustard and some salt and pepper. Whisk it together and add the bread. Toss everything to coat, then add the tomatoes, cucumbers, string beans and onions. Toss everything again. Let the salad marinate 30 minutes before serving.
Check the seasoning before serving, adjusting with more salt and freshly ground pepper if needed.
Recipe courtesy of Nancy Fuller