Cut the onion into square pieces and slice the green chili.

Drain the canned tuna and save the oil for later use.

Mix sugar, gochujang, chopped green onion, minced garlic, sesame oil, and the saved tuna oil to create the sauce.

Heat a pan over high heat, add vegetable oil, and stir-fry the onion until golden brown.

Add the prepared sauce to the pan and mix well.

Add the drained tuna and stir-fry until combined. Add the green chili and mix again.