Combine soy sauce, mirin, ginger in a large bowl and mix well.
Mix in chicken and marinate for at least 30 minutes. (see note 2)
When ready to cook, add oil into a hot heavy-based pan on high heat.
Sear chicken thighs on both sides until brown (around 2 minutes on each side).
Pour reserved marinade into the pan, lid on and turn the heat down to low and simmer for about 4 - 5 minutes until chicken is cooked.
Serve with a bowl of steamed rice and some sauteed broccoli.