Shred the cabbage.
Finely chop the onion and green onion.
Heat cooking oil in a pan and sauté the onion and green onion.
Add the cabbage and stir-fry over medium heat.
Add gochujang (Korean chili paste), red pepper powder, soy sauce, minced garlic, and sugar, then stir-fry.
Drain the oil from the canned tuna and add it to the pan. Stir-fry together.
Spoon the stir-fried mixture over the rice.
Sprinkle seaweed flakes and pepper to taste.