If you want to do it from scratch here's the rough recipe I use at the moment.
100ml dark soy
60g brown sugar
1/2" ginger minced
2-3 cloves garlic, minced
1 tsp sesame oil (use the 100% toasted sesame oil, not the cheap stuff; it doesn't taste of anything)
1 tsp veg oil
40ml mirin
15ml honey (I use agave to keep it vegan)
100ml water mixed with 1tbsp corn flour
Heat the veg oil/sesame oil on low, cook out the garlic and ginger for 2-3 mins very gently (the sesame oil will burn on high heat). Add the soy, sugar, mirin and honey. Bring to just under boiling and make sure the sugar has all dissolved. Add the water/corn flour slurry and whisk as it comes to the boil.
Allow to cool - this can just be used as a dip or sauce as well as in cooking.
For the chicken cut thighs into small chunks, 150g per portion roughly. Toss with 1/2tsp bicarbonate soda and marinate for 20 mins, then wash off. This will tenderize the chicken.
Season with salt, MSG, white pepper and toss in corn flour. Fry off in hot oil (180c) for 3-4 mins. Take out and drain off excess oil.
Stir fry some spring onion, garlic, red pepper etc. What ever veggies you want, add the teriyaki (3-4tbsp) and reduce for 30s-1 min, add the chicken and toss together.
You should have something similar to restaurant Teriyaki chicken.
