In a large mixing bowl, combine the shredded lettuce, shredded carrots, sliced cucumber, imitation crab meat, and chopped green onions. Toss gently to mix the ingredients evenly.
In a separate small bowl, whisk together the mayonnaise, rice vinegar, sesame oil, sugar, soy sauce, salt, and black pepper until smooth and well combined.
Pour the dressing over the salad mixture and toss gently until all the ingredients are coated with the dressing.
If time allows, chill the salad in the refrigerator for about 15-30 minutes to enhance the flavors.
Before serving, sprinkle sesame seeds on top for garnish, if desired. Serve immediately.