Steam green beans in a covered pot with half an inch of boiling water for 3-4 minutes. Cold shock them by running them under cold water and drain well.
In a large mixing bowl, mix up the mustard, honey, vinegar, salt and black pepper with a whisk. Once the ingredients are well combined, drizzle the EVOO in a slow and steady stream while continuously whisking. Add the cooked and shocked beans to the bowl with the dressing along with scallion and radishes, and toss to coat.