Cut tuna into bite-sized pieces.
Dice cucumber and avocado into cubes.
Place rice or cauliflower rice in a bowl.
Top with sliced tuna, cucumber, and avocado.
Mix soy sauce, sesame oil, and lemon juice to make dressing.
Drizzle the dressing evenly over the ingredients.
Finish with seaweed, chopped green onion, and toasted sesame seeds.