Usually chicken teriyaki (or chikiteri as it's abbreviated sometimes) is made from whole chicken thigh pieces, but I prefer to cut the meat up in advance for bento use - the smaller pieces cook faster, and I don't have to deal with slicing hot cooked meat early in the morning.

The chicken can be marinated from the night before or just briefly in the morning. You can also make this in some quantity and freeze the cooked pieces - since you are using thigh meat, the pieces won't dry out so easily after defrosting like white meat can.