Precooking the green beans in the microwave par-cooks them and helps them keep their pretty green color. You can also cook them in boiling salted water for 3-4 minutes, blanch them in ice water, or throw them straight into the mushroom miso base. The green beans in the recipe come out slightly al dente because I like a little bite to my beans. If you like your green beans soft, I recommend adding 1-2 minutes to the microwave cook time.