Drain the tuna and empty it into a small bowl. Add the kewpie mayo and sriracha and use a fork to mash everything together. Set aside.
Thinly slice the cucumber, avocado, and green onion.
To assemble, add the mixed greens and white rice to a bowl. Top with the tuna, cucumbers, avocado, and seaweed. If desired, top with sushi ginger, green onions, and chili crunch. Enjoy!!