Gather all ingredients.
Roughly chop the onion.
Julienne the carrot (cut into long thin strips).
Remove and discard the first outer layer of cabbage leaves. Separate the remaining leaves. For each leaf, cut out the thick, hard vein from the center of the leaves, only using the tender outside of the leaves. Tear or cut into large pieces. Use most or all of the cabbage. It will seem like a lot, but it cooks down.
Chop your meat into bite-size pieces, set aside. Slice the kamaboko (steamed fish cake), set aside.
For udon: Discard any sauce that came with the noodles (you'll use the soup base you made). Follow boiling instructions on the package. After noodles are boiled, drain and rinse in cold water. Rinsing in cold water stops the cooking process and removes some of the starch so the noodles do not stick together. Set aside until ready to use.
Meanwhile, in a wok or deep frying pan, heat oil over medium-high heat. Add your choice of meat and cook until almost cooked through about 5 minutes. Add the onions and cook until translucent and soft. Add the carrots, kamaboko, and cabbage. With tongs, gently toss the ingredients as the cabbage begins to wilt.
Add most or all of the soup base (depending on how soupy you want your dish) to the wok or frying pan. Continue to toss with tongs to coat the vegetables evenly and heat up the soup. Add the cooked udon noodles, and toss gently to allow the noodles to absorb some of the soup, about 5 minutes.
Serve and garnish with green onions.