Slice the onion thinly.

Add the canned tuna with its oil and the sliced onion to a frying pan. Stir-fry over medium heat.

Once the tuna oil coats the onion, add the seasoning ingredients (water, soy sauce, dashi powder) and mix well.

Bring the mixture to a boil, then cook for 2 minutes. Pour the beaten eggs evenly over the mixture.

Once the eggs start to set, turn off the heat, cover the pan, and let the residual heat cook the eggs to a soft consistency.