1 part low-sodium soy sauce (we prefer Kikkoman)
2-3 part water
brown sugar to taste
large pulverized onions (we use a food processor or chopper)
fresh garlic buds (crushed)
fresh ginger root (peeled and crushed/ground)
frozen, boneless chicken thighs (Sysco has boxes of flash-frozen thighs for cheap if you're cooking for a big crew)
Calrose white, short-grained rice
Mix the soy sauce and water first. For a 3 lb bag of thighs, we mix up about 1/3 of a 26 cup bowl with the water/soy sauce mix first in a large tupperware bowl. I've never measured the exact amounts but it doesn't really matter - it should be to taste. Add the brown sugar and stir until it's slightly sweet. We add about a fistfull or so for a large bowl. Add the onions, garlic and ginger root. Again, it's to taste, but we like the mixture to be fairly full of these to add additional flavor.
Once you're satisfied with the flavor of the sauce, dump the frozen chicken in and let it sit overnight (or about 6 hours if you're prepping on a schedule) in your fridge. The longer you let it soak, the better. If you're only doing it for a few hours, you may not need to refridgerate it. We often do this in a cooler (for mutual activities) and don't refridgerate it at all - just remember to close the lid!
Once it's done marinating, BBQ it (all our Samoan and Tongan friends only use charcoal - gas doesn't give it the right flavor). We pull each piece out dripping wet and baste the others that are on the grill already as you put the new one on. Repeat for all pieces. Flip them often - you're not looking for blackened or dry, just bouncy, juicy meat. If you cook it too long, it'll be too dry. When they're done, toss them in a pan/bowl with a bed of shredded, slightly boiled cabbage on the bottom. Put a lid on to keep them hot and steam the cabbage a bit. It'll absorb the juices too and tastes amazing with the meat and rice.
We use this a lot for our "youf" (Samoan for 'Youth') in our ward. It can easily be made in a large cooler or multiple coolers for any occasion and tastes great with Calrose white rice, and macaroni salad in the true island way. Makes an awesome beach bbq bonfire dinner.