To shred the cabbage, trim the core off of the end so that it sits steady without rolling around. Cut in half vertically and then cut each half in half again to make quarters. Remove any remaining core and thinly slice to make long, thin strands. Set aside.
In a large bowl, add all of the dressing ingredients and whisk to combine. Taste and adjust seasonings. If the dressing is too tangy, add a pinch of sugar to balance it out. At this point, you can also add more of whatever you like. If you like more soy, add it. More vinegar? Add it! The beauty of these kinds of salads is that you can make them to suit your own tastes.
Once the dressing is done, add in the veggies and toss to thoroughly coat everything. Almost immediately, the cabbage will start to break down and wilt. Stir a few more times, cover and put in the refrigerator to chill for at least 30 minutes. If possible, give it a stir every 10 minutes or so.
Before serving, taste and adjust the seasonings again and add salt and/or pepper, if needed. Serve with extra green onions on top for garnish.