Slice the cabbage thinly and set aside.
Slice the onion thinly.
Chop the green onion into small pieces.
Heat cooking oil in a pan and sauté the green onions and onion.
Add the cabbage and stir-fry until wilted.
Drain the tuna and add it to the pan, stir-frying together.
Season with soy sauce, oyster sauce, and pepper.
Serve the stir-fried ingredients over warm rice.