Shred the cabbage and set aside.
Slice the onion and chop the green onion.
Heat olive oil in a pan, then sauté the onion and green onion.
When the onion becomes translucent, add the cabbage and stir-fry.
Drain the oil from the canned tuna, add the tuna to the pan, and stir-fry together.
Season with soy sauce and pepper.
Spoon the stir-fried mixture over rice to serve.