In a large bowl, combine the diced cucumbers, avocados, imitation crab, red onion, sesame seeds, and chives.
In a small bowl, whisk together the rice vinegar, mayonnaise, soy sauce, sesame oil, sugar, salt, and pepper until smooth.
Pour the dressing over the salad ingredients and gently toss to combine, being careful not to mash the avocado.
Taste and adjust seasoning if needed, adding more salt or vinegar according to your preference.
Serve immediately or cover and refrigerate for up to 30 minutes before serving for slightly chilled salad.