Cut the baby cabbage into bite-sized pieces.
Slice the onion thinly and cut the red chili diagonally.
Drain the oil from the tuna using a sieve.
In a bowl, add the baby cabbage, onion, red chili, and tuna.
Add gochujang (Korean chili paste), soy sauce, sesame oil, minced garlic, vinegar, and sesame seeds, then mix well.
Arrange beautifully in a dish.