Wash the cabbage thoroughly and shred it.
Slice the onion thinly.
Heat olive oil in a pan and sauté the onion.
When the onion becomes translucent, add the cabbage and stir-fry.
Once the cabbage softens, add the tuna and continue to stir-fry.
Season with soy sauce and pepper.
Place the stir-fried ingredients on top of rice and sprinkle sesame seeds to finish.