Slice the cucumbers thinly and lay them on a paper towel to remove excess moisture.
Cut the avocado and imitation crab into small, bite-sized chunks.
In a mixing bowl, whisk together Japanese mayo, soy sauce, rice vinegar, sesame oil, and sriracha.
Place the cucumber, crab, avocado, green onions, and rice (if using) into a large mixing bowl.
Pour the dressing over the cucumber salad and toss gently to combine.
Top with sesame seeds and crumbled nori before serving.
