Mix together the fish sauce, sugar, rice wine vinegar and grated ginger. Pour over the chicken, mix well and allow to marinate for at least 20 minutes.
Heat the cooking oil in a pan. When very hot (you’ll see smoke start to appear), drain the chicken (reserve the marinade) and add to the oil. Cook, stirring and tossing alternately, until lightly browned around the edges. Scoop out and keep warm.
In the remaining oil in the pan, sauté the garlic, ginger, chives, lemongrass and chilies until fragrant, about 45 seconds.
Return the chicken to the pan. Add the pineapple chunks.
Pour in the marinade. There will be very little liquid but, trust me, that little liquid is packed with flavors. So, use it.
Without lowering the heat, stir fry for a couple of minutes to cook the chicken through. The pineapple chunks should expel enough juices in which the chicken can cook completely.
Taste the sauce (there will be very little). Add more fish sauce, sugar or rice wine vinegar, as needed.
Sprinkle with snipped cilantro to garnish.
Serve your Vietnamese chicken and pineapple stir fry hot with rice.