STEP 5/7
Add 2T of soy sauce, 1T of sugar, and 0.5T of oyster sauce and stir-fry well.
If there is no oyster sauce, it can be omitted.
Keep stirring and stir-fry well. Turn off the heat when you think the onion is cooked as it becomes transparent.
STEP 6/7
Lastly, if you sprinkle sesame seeds and put them in a bowl, it becomes a side dish of stir-fried tuna onions.
STEP 7/7
If you have a little more time, don't pop the egg yolk, make a fried egg, put rice in a bowl, put stir-fried tuna onion, and mix it with the yolk and eat it like a rice bowl.