Finely chop the cabbage.
Dice the onion.
Heat oil in a pan and sauté the onions.
When the onions become translucent, add the cabbage and stir-fry together.
Drain the tuna and add it to the pan, stir-frying together.
Add the rice and mix everything evenly while stir-frying.
Season with soy sauce, salt, and pepper.
Serve in a bowl to finish.