Japanese people tend to use chicken thigh rather than breast meat for the extra flavour, but both will work fine.
Add some dashi stock to a pan and heat it up before adding a spoonful each of mirin and soy sauce plus a pinch of sugar.Now is also a good time to start cooking your rice separately so that it is ready for when you finish cooking the dish.
Once the soup has been simmering for a few minutes, add your pieces of chicken and cook them until the chicken has cooked through thoroughly.
Once the chicken is done, chop up a whole onion into thin slices and add them to the pan.
Beat your eggs in a bowl (with chopsticks if you are an expert), then pour into the pan and let it cook for a few minutes.
Try not to let the egg cook too much, a slightly runny texture is the preferred way to serve oyakodon.
When the eggs are done, turn off the heat and pour the egg and chicken over a bowl of freshly boiled white rice.
Garnish with some finely sliced spring onions and possibly a little Japanese mayonnaise before serving, enjoy!