Finely chop the onion and green onion.
Heat cooking oil in a pan and sauté the onion and green onion.
Add tuna and stir-fry, then add gochujang (Korean red chili paste) and red pepper flakes, mixing well.
Add rice and stir-fry together with the ingredients.
Season with soy sauce and pepper to taste.
Finish by sprinkling sesame seeds on top.