Cut the chicken fillet into strips. Marinate in soy sauce in the refrigerator for 30 min.
Peel and dice the onion.
Heat the vegetable oil over medium heat in a large pan. Add the diced onion and sauté for 2-3 min until softened. Add the marinated chicken strips and fry over medium heat, stirring occasionally, for 3-4 min until the chicken begins to color.
Add the coconut milk and continue cooking over medium heat for 10 min.
Check that the chicken has reached an internal temperature of 74 °C (165 °F).