Dice tofu, cucumber, onion, and avocado into cubes.
Drain the oil from the canned tuna using a sieve.
In a bowl, add tofu, tuna, cucumber, onion, and avocado.
Add soy sauce, sesame oil, lemon juice, and a pinch of chili powder, then mix.
Spoon the mixture over rice and top with seaweed and sesame seeds to finish.