Open the can of tuna and drain out the water or oil.
Thinly slice the onion into half moons. Stir fry over medium-high heat until the onions just start to brown.
Add the tuna and turn the heat down to medium. Stir to mix.
Season with the sugar and soy sauce. Cook for another 1-2 minutes until everything is well mixed and tasty.
Remove to a serving dish. Top with green onions (optional). It is ready to eat! Enjoy hot, with a big bowl of rice ^_^