1 Bring a large pot of water with a steamer basket to a boil, add green beans and steam for 5 minutes. Transfer to a serving bowl. 2 Toast the walnuts in a small dry skillet over a medium heat until they become fragrant, about 2 minutes, and then transfer them to a small bowl.3 Add the parsley and onion to the walnuts and stir to combine4 In another small bowl, whisk together the oil, vinegar and mustard. 5 Toss the dressing with the green beans, top with the walnut mixture and season with salt and pepper6 Serve warm or at room temperature.