Summarize the following:
Chicken yakitori is traditionally cooked on a charcoal grill. Light these grills 30–45 minutes before you cook the chicken, waiting until the charcoal turns white and the flames die down. You may use a gas barbecue instead, which could only require 15–20 minutes of heating before use. If you plan to marinade the ingredients, which is optional, you may wish to wait until that step before you light the barbecue.  Binchotan charcoal is favored by yakitori chefs due to its long burning time and minimal odors. However, a fire starting pan may be required to light binchotan charcoal.  While grilling is by far the most common method of cooking yakitori in Japan, instructions are also included below for frying pans and broilers. Submerge about ten 15 cm (6 inch) skewers in cold water before you start food preparation, so they won't catch fire on the grill. Bamboo skewers called teppo gushi are usually used to make yakitori, since they have flattened sides that prevent the skewers from rolling on the grill. However, you can use any design of bamboo or wooden skewers. Cut off the brown ends of the scallions and throw them away. Chop the remaining white and light green sections into chunks about 2 cm (3/4 inch) wide. Chop larger pieces in half lengthwise if necessary to keep pieces roughly the same size. Optionally, the thinner, dark green pieces can be chopped finely and used as garnish on the final dish. Chopping the scallions first allows you to use the same knife and cutting board for the chicken. If you cut the chicken first, wash the knife and cutting board immediately afterward, to reduce the chance of contamination from raw meat. Chop 450g (1 lb) chicken breast or chicken thighs into bite size, easily skewered pieces, about 2.5–3cm (1 inch) on each side. To skewer a chicken piece, fold it in half, hold against a cutting board, and pierce it at a 45º angle with the skewer. Alternate between skewering chicken and scallion pieces for each skewer. Leave a little space at the ends of the skewers, to prevent pieces from falling off and so people can hold them. If you have the time, and prefer a stronger taste of yakitori sauce, you may set aside some sauce in a shallow container and marinade the skewers in it for 15–30 minutes. Throw away the marinade afterward, as it is likely contaminated with bacteria from the raw meat. Warning: always keep the sauce for marination separate from the sauce you will use to brush the skewers during cooking, to avoid the high risk of contamination from raw poultry.
If using a barbecue, light it in advance. Soak the wooden skewers for 30 minutes. Cut the scallions. Cut the chicken into bite sized pieces. Skewer the chicken and scallions. Marinate the skewered ingredients (optional).