Prepare the vegetables: remove outer cabbage leaves, quarter the cabbage, remove the core, then stack and thinly slice across the grain into fine ribbons. Slice cucumbers thinly (seed out if watery), shred the carrot, and slice the scallions. Chop herbs.
Salt and massage the cabbage: place the sliced cabbage in a large bowl, sprinkle ½ teaspoon salt over it, and massage with clean hands for 2–4 minutes until it softens slightly and releases a bit of liquid. This makes the cabbage more tender and flavorful.
Make the dressing: in a jar or small bowl combine vinegar, Dijon mustard, honey (if using), grated garlic (if using), ½ teaspoon salt, and pepper. Whisk while slowly streaming in the olive oil to emulsify. Stir in toasted sesame oil if using. Taste and adjust seasoning.
Combine salad components: add cucumbers, carrot, scallions, and herbs to the massaged cabbage. Pour about two-thirds of the dressing over the vegetables and toss thoroughly to coat.
Rest to marry flavors: let the salad sit 5–15 minutes at cool room temperature so the dressing melds with the vegetables. For a stronger meld, refrigerate up to 30 minutes; if making longer ahead, keep dressing separate and toss before serving.
Finish and serve: taste and adjust salt and acid. Add remaining dressing if needed. Scatter toasted seeds or nuts over the top and give a final gentle toss. Serve chilled or at cool room temperature.