Mix all the sauce ingredients together in a small pan. Bring to a boil, then reduce the heat and simmer for 10 minutes, or unit the sauce has thickened.
Cut the chicken into 1 inch cubes. Cut the spring onions into 1" long sticks.
To grill, preheat the grill to high. Oil the rack and spread the chicken cubes on it. Grill both sides of the chicken until the juices drip, then dip the pieces in the sauce and put back on the rack. Grill for 30 seconds on each side, repeating the dipping process twice more.
Set the chicken aside and keep warm. Gently grill the spring onions until soft and slightly brown outside. Do not dip. Thread about four pieces of chicken and three spring onion pieces on to each of eight bamboo skewers.
Alternately, to cook on a barbecue, soak eight bamboo skewers overnight in water. this prevents the sewers form burning. Prepare the barbecue. Thread the chicken and spring onion pieces on to the skewers as above. Place the sauce in a small bowl with a brush.
Cook the skewered chicken on the barbecue. Keep the skewer handles away from the fire, turning them frequently until the juices star to drip. Brush the chicken with sauce. Return to the coals and repeat this process twice more until the chicken is well cooked.
Arrange the skewers on a platter an sprinkle with shichimi togarashi or sansho, or serve with lemon wedges.
Credits Japanese Cooking - by Emi Kazuko and Ysuko Fukuoka