Wash the cabbage thoroughly and cut it into thin strips.
Slice the onion thinly.
Heat cooking oil in a pan and sauté the onion.
Add the cabbage and stir-fry together.
When the cabbage softens, add the tuna.
Season with soy sauce, salt, and pepper.
Place the sautéed cabbage and tuna on top of rice.
Finish by sprinkling mayonnaise and seaweed flakes as desired.