Blanch broccoli in boiling water for 90 seconds until bright green and just barely tender.
Transfer immediately to an ice bath, cool for 2 minutes, drain and pat dry.
Whisk all dressing ingredients together. Taste and adjust — more vinegar for brightness, more soy for depth, more honey if it needs balance.
Combine broccoli, cabbage, carrots, and most of the scallions in a large bowl, reserving some scallion for topping.
Pour dressing over vegetables and toss well.
Rest for at least 15 minutes before serving.
Top with reserved scallions and sesame seeds.
Store sesame seeds separately if meal prepping so they stay crunchy.