Make the dressing: Whiz the carrots, shallot and ginger in a blender or food processor until finely chopped. Scrape down the sides, then add the miso, vinegar and sesame oil. While the machine is running, slowly drizzle in the grape seed oil and the water.
Assemble salad: Trim and chop lettuce into small wedges. Arrange on a platter. Scatter onion and avocado on top. Sprinkle some flaky sea salt and black pepper over the salad. Dollop with plenty of dressing and serve with remaining dressing on the side. Optionally, add strips of purple and yellow carrot, snipped chives, and toasted black and white sesame seeds for garnish.
