Slice half an onion and chop the green onion, reserving some for garnish.

Beat 2 eggs and scramble them quickly in a pan with cooking oil. Remove while slightly undercooked for a soft texture.

Drain half the oil from the tuna can and stir-fry the tuna in a pan without additional oil. Add a pinch of black pepper.

In a pan with cooking oil, stir-fry the onion and green onion until translucent.

Mix soy sauce, sugar, mirin, and sesame oil beforehand. Add this mixture to the onion stir-fry along with 3 tbsp of water and cook until slightly reduced.

Layer the cooked rice in a bowl, followed by the onion stir-fry, tuna, and scrambled eggs.