Wash the cabbage thoroughly and slice it thinly.
Slice the onion thinly and chop the green onion.
Add cooking oil to a pan and stir-fry the onion and green onion.
Add the cabbage and stir-fry until it softens.
Drain the oil from the tuna can and add it to the pan, stir-frying together.
Season with soy sauce, salt, and pepper.
Place the stir-fried cabbage and tuna mixture over rice.