Shred the cabbage thinly
Slice the onion thinly
Heat cooking oil in a pan and stir-fry the onion and cabbage
Season with salt and pepper
Drain the oil from the canned tuna and add it to the pan, stir-frying together
Place the cooked mixture over rice
Finish by drizzling some soy sauce and sesame oil, then sprinkle with sesame seeds