Cut the cabbage into bite-sized pieces.
Julienne the onion and green onion.
Heat some cooking oil in a pan and sauté the onion and green onion.
Add the cabbage and stir-fry together.
Add the canned tuna and mix well.
Add gochujang (Korean chili paste), soy sauce, minced garlic, and pepper, then stir-fry everything together.
Place the stir-fried mixture over rice and sprinkle with sesame seeds.