Prepare all the ingredients by chopping the onion, green onion, and chili pepper.

Heat oil in a pan and sauté the chopped onion until translucent. Add a small amount of minced garlic if desired.

Add the gochujang sauce mixture (gochujang, sugar, soy sauce, and rice wine) to the pan and stir well.

Drain the oil from the canned tuna and add the tuna to the pan. Stir to combine.

Add the chopped chili pepper and green onion to the pan and mix well.