I made this dish as a lunch after Christmas since we made a large rib roast and had leftovers. In Japan, "Beef bowl" or "Gyudon"牛丼 is a popular fast food. One example is "Yoshino-ya" 吉野家 made of braised thinly sliced beef and onion in a soy sauce based broth (with other "secret" ingredients) placed over a bowl of rice. While braised beef is fairly common, roast beef is not. Roast beef bowl, however, is also getting more popular in Japan. Some appears excessive in terms of the amount of meat they put on the rice. I made a much tamer version. I thinly sliced the rib roast choosing the medium rare part. This is a small bowl and I served it with miso soup.
The Japanese version is often topped with an egg (either raw or onsen-tamago) but I topped this with thinly sliced cucumber, sweet onion and blanched green asparagus.
The miso soup was made of scallion, aura-age and tofu.
For the sauce, I just mixed soy sauce, mirin and prepared horseradish.
This was a just perfect lunch for us.