Wash the cabbage thoroughly and cut it into bite-sized pieces.
Julienne the carrot thinly.
Slice the onion thinly.
Drain the oil from the canned tuna and set aside.
Heat cooking oil in a pan, then add the onion, carrot, and cabbage and stir-fry.
When the vegetables begin to soften, add the tuna and mix well while stir-frying.
Season with salt and pepper.