Thinly slice the cabbage and set aside.
Julienne the onion and carrot.
Heat cooking oil in a pan and stir-fry the onion and carrot first.
Add the cabbage and stir-fry until it softens.
Add the tuna (drained) and stir-fry together.
Season with soy sauce and pepper.
Serve in a bowl, like a rice bowl, to finish.