In a large bowl, combine 4 cups shredded Napa cabbage, 1 shredded carrot, 4 chopped green onions (white and green parts), and 3 tablespoons toasted sesame seeds.
In a small bowl, whisk together 3 tablespoons toasted sesame oil, 2 tablespoons rice vinegar, 1 teaspoon sugar, and 1/2 teaspoon kosher salt until the sugar begins to dissolve.
Drizzle the dressing evenly over the cabbage mixture.
Toss the slaw gently with tongs or two forks until everything is evenly coated.
Taste and, if desired, add a small additional amount of sugar, kosher salt, or sesame oil a little at a time, then toss again.
Serve right away, or transfer to an airtight container and refrigerate for up to overnight.