Serve over brown rice for a hearty, extra delicious meal. Plan to soak the rice for 3-4 hours before cooking (@ 40 minutes in my rice cooker) and rinse well in a strainer before cooking (rinses off excess starch). This makes for much softer, more edible rice.
5 (or more) hours before you want to serve the dish, soak the rice in a saucepan of lukewarm water. Make sure there are a couple inches of water above the rice. After it's soaked for at least 4 hours (right around the time to start prepping the marinade/chicken) transfer the rice to a large strainer and rinse it under the tap to remove excess starch. Put rice in a rice cooker with 2 T butter and 1/2 tsp salt and 4 c water and cook until done. It should be ready around the same time as the chicken.
In a bowl, whisk together the grated ginger, chopped garlic, brown sugar, fish sauce, water, rice wine vinegar, soy sauce, black pepper and crushed red chile flakes.
Trim any excess fat off the chicken thighs and set aside in the bowl with the marinade.
Heat the oil in a large frying pan over medium heat. Add the chopped onions and sauté for 2-3 minutes. Add the scallions and sauté for another 3 minutes or until the scallions have softened.
Add the thighs and the brown sugar mixture to th pan. Turn the heat to high and bring to a boil. As soon as it comes to a boil, reduce the heat to low and simmer for 25-30, turning the thighs at 15 minutes, until the thighs are fully cooked.
Remove the thighs from the pan and cover with foil to keep warm. Increase the heat to high and reduce the sauce until it is slightly thickened and resembles a bubbling caramel sauce. Serve the chicken in the sauce, garnished with the cilantro, if using.