Teriyaki chicken with ginger mash

Ingredients

• 6 chicken thigh fillets, halved crossways
• 2 tablespoon soy sauce
• 2 tablespoon mirin seasoning
• 1 tablespoon brown sugar
• 4 medium (800g) potatoes, chopped
• 40 gram butter, chopped
• 1/4 cup warm milk
• 3 centimetre piece fresh ginger, peeled, grated
• 3 green onions, thinly sliced
• cooked green beans, to serve