Shred the cabbage and thinly slice the onion.
Heat olive oil in a pan and sauté the onion.
When the onion becomes translucent, add the cabbage and continue to sauté.
Once the vegetables are cooked, drain the tuna can and add the tuna to the pan.
Season with soy sauce and pepper to taste.
Spoon the sautéed mixture over rice to finish.