Shred the cabbage.
Slice the onion.
Add olive oil to a pan and sauté the onions.
When the onions turn translucent, add the cabbage and continue to sauté.
Drain the oil from the canned tuna and add the tuna to the pan, stir-frying together.
Season with soy sauce and pepper.
Place the stir-fried mixture over rice to finish.