Prepare an onion and a can of tuna; thinly slice the onion.
Add cooking oil to a pan and sauté the onions.
When the onions turn translucent, add the tuna and stir-fry together.
Season with soy sauce and sugar to taste.
Place the stir-fried onion and tuna over cooked rice.
Sprinkle seaweed flakes and sesame seeds on top as desired.