In a large glass measuring cup, whisk together all the ingredients for the sauce, except for the tapioca starch.
Heat the olive oil (or other healthy cooking fat of your choice) in a large wok or skillet set over high heat. When the pan is nice and hot, add the pieces of chicken, sprinkle them generously with salt and let the meat cook until it gets nice and golden all around, about 10 to 12 minutes.
Once the chicken is fully cooked, add the bell peppers and onions and continue cooking for about 1 minute, until the veggies are just slightly softened and fragrant; throw in the drained pineapple chunks and mix well.
Whisk the tapioca starch in the sauce and then pour it into the skillet. Bring to a full boil, stirring continuously until the sauce is thickened, then remove from heat and serve with a side of steamed rice, garnished with a pinch of finely chopped green onions, if desired.