Cut the cabbage and green onion into bite-sized pieces.
Heat cooking oil in a pan and sauté the green onion until fragrant.
Add the cabbage and stir-fry over high heat.
Add the tuna (after draining the oil) and mix well while stir-frying.
Add gochujang, soy sauce, sugar, and minced garlic to make it spicy.
Add a little water and stir-fry until the cabbage softens, then turn off the heat.
Spoon the stir-fried mixture over rice, sprinkle with sesame seeds, and serve.