Thinly slice the cabbage.
Slice the onion.
Heat olive oil in a pan and sauté the onion.
Add the cabbage and season with salt and pepper, then stir-fry.
Drain the oil from the canned tuna using a strainer.
Place the tuna on top of the sautéed vegetables.
Drizzle soy sauce and sprinkle sesame salt to finish.