Combine the soy sauce, sugar and sake or dry sherry in a pan. Crush the garlic and the ginger with the side of a wide bladed knife and add to the pan. Cut one spring onion into 4 cm lengths and then shred the pieces lengthwise and add to the mix. Bring to the boil and simmer for a few minutes until slightly thickened. Transfer to a small dish to take to the barbecue and reserve a little as a dipping sauce for later.
Cut the chicken into evenly sized pieces about 3 cm cubes. Cut the pepper into 3 cm squares and then cut the spring onions into 3 cm lengths.
Push the chicken onto the pre-soaked skewers. First a piece of chicken then a piece of spring onion, chicken, pepper, spring onion then finally a piece of chicken. Keep the food towards the pointed end of the skewer so that not much skewer is showing and it has a long handle at the other end.
Make up a foil guard and place on the grill. Position the skewers so that the meat is over the heat and the skewers are over the guard, this will prevent the skewers burning.
Cook until the chicken is cooked about halfway through then turn and cook the other side. Baste with the marinade and then baste a few more times as you continue to turn and cook the chicken. Be careful not to overcook. The marinade will caramelise into a nice golden brown colour. Serve with a little of the marinade reserved earlier as a dip.
The marinade can also be succesfully used for Salmon. Simply cut the salmon into 3 cm cubes and marinade for about 30 minutes.