Wash the napa cabbage thoroughly and cut into bite-sized pieces.
Drain the oil from the canned tuna using a sieve.
In a bowl, add napa cabbage, tuna, chopped green onion, and minced garlic.
Add red pepper flakes, soy sauce, sesame oil, and pepper, then gently mix everything together.
Transfer to a plate and sprinkle with sesame seeds to finish.