Ah-Kung's Stir-Fried Chicken with Bell Peppers & Soy-Vinegar Sauce

My maternal Grandpa (Ah-kung) used to make this dish to perfection. I can't quite replicate it, but here's my best rendition. Ah-kung was originally from Fujian province in China, and tended to use a liberal amount of vinegar, soy and sugar in his cuisine (spice was not part of the regimen). I have such fond memories of his perpetually happy countenance and super cool laid-back personality. I miss him dearly.