In a large bowl, combine the sliced cucumbers, shredded imitation crab meat, diced avocado, and chopped green onions.
In a separate small bowl, whisk together the rice vinegar, soy sauce, sesame oil, sugar, salt, and pepper until the sugar is dissolved.
Pour the dressing over the cucumber mixture and gently toss to combine, being careful not to mash the avocado.
Sprinkle sesame seeds on top for garnish.
Chill the salad in the refrigerator for at least 15 minutes before serving to allow the flavors to meld.