Wash the cabbage thoroughly and shred it.
Slice the onion and carrot thinly.
Drain the oil from the canned tuna and set aside.
Add cooking oil to a pan and stir-fry the onion, carrot, and cabbage.
When the vegetables are softened, add the tuna and mix well.
Season with soy sauce, oyster sauce, and pepper.
Spoon the stir-fried mixture over rice to complete the rice bowl.