Cut the chicken into 2.5cm cubes. Thread the chicken cubes onto the soaked skewers, alternating with the spring onion.
In a small saucepan, combine the mirin, soy sauce, sake and sugar. Bring to the boil. Reduce heat and simmer for 5 minutes. Reserve half of the sauce for dipping.
Heat a grill pan over high heat and lightly brush with vegetable oil. Cook the skewers, 7 to 10 minutes per side, basting frequently with half of the sauce. Remember to baste frequently for best flavour!
Serve with extra sauce on the side, and with white rice if desired.