Shred the cabbage.
Slice the onion thinly.
Heat cooking oil in a pan and sauté the onion.
When the onion becomes translucent, add the cabbage and stir-fry together.
Once the vegetables have softened, add the tuna and stir-fry.
Season with soy sauce, sugar, and cooking wine.
Place the stir-fried mixture over rice and sprinkle with sesame seeds.