Cut tuna sashimi into bite-sized pieces.
Dice avocado, cucumber, onion, and other vegetables finely.
Place rice in a bowl.
Top the rice with tuna, avocado, and vegetables.
Make a sauce with soy sauce, sesame oil, lemon juice, and a bit of wasabi.
Drizzle the sauce evenly over the ingredients.
Finish by sprinkling seaweed and sesame seeds on top.