Cut the chicken into bite-sized pieces.
Dice the potatoes into cubes.
Slice the onion thinly.
Add cooking oil to a pan and stir-fry the chicken.
Add potatoes and onion; stir-fry together.
Season with soy sauce and sugar.
Pour in water, cover, and simmer over medium heat.
When the potatoes are cooked, turn off the heat and drizzle sesame oil on top.