Namul (or namuru as it's called in Japan) is a very versatile vegetable side dish from Korea. It's one of the key ingredients of a bibinbap but I make namul much more frequently than I make bibinbap. Various vegetables are quickly boiled or blanched, and then dressed with a simple dressing of sesame oil and salt. It's a great way to eat a lot of vegetables, since the boiling or blanching shrinks down the mass quite a lot. The compactness makes it a perfect bento side dish. It's so good for you, but tastes great!
I make namul with all kinds of vegetables, including the most commonly used one, bean sprouts. But at this time of year I like to make it with brightly colored spring greens. The toasty sesame oil dressing is a perfect foil to the bitterness of many of these greens. Here I've used three kinds of greens that are easily available to me, but do use whatever you have around where you live. I've used the dark green, mildly bitter leaves of a puntarelle or catalogna (which I used to think was cima de rapa), spinach leaves, and lamb's lettuce (also known as mâche - see more about ithere). If I were in Japan at this time of year I'd use spinach, nanohana, and maybe some komatsuna. I've listed some green vegetables that would work below.