In a bowl, combine the chicken, garlic powder, soy sauce, oyster sauce, honey, brown sugar, apple cider vinegar, and tomato paste. Toss everything to coat well. Marinate the chicken for at least an hour or overnight.
Meantime, heat the skillet with oil. Add the pineapple slices and brown for a minute on each side. Remove from the pan and set them aside.
Use the same pan, add the marinated chicken, sear for 1-2 minutes on each side or until golden brown. Remove from the pan and set them aside.
Add the onion into the same pan, cook until caramelized. Add the garlic, saute until fragrant. Add the chicken back into the pan, and add the remaining marinade also. Add the chicken broth and bay leaves. Cover, lower the heat, simmer for 2 minutes. Meantime, combine the cornstarch and water, stir until cornstarch dissolved (this is the slurry).
Add the slurry, stir, cook until the sauce thickened, about a minute.