Put the string beans and frozen edamame into a steamer basket and steam them for 4 minutes. Transfer the beans to a large bowl and put them into the refrigerator to cool for 15 minutes or longer.
In a small bowl whisk together the oil, vinegar, apricot preserves, sugar and ginger. Add the black beans and scallions to the other beans, drizzle with dressing, and toss to coat. Season with salt, to taste.