In a bowl, combine the cubed chicken thighs with Shaoxing wine, salt, and cornstarch. Mix thoroughly and marinate for 15 minutes.
While the chicken marinates, cut the onion into thick wedges and slice the scallions into ½-inch pieces, separating the whites and greens.
In a small bowl, combine dark soy sauce, light soy sauce, oyster sauce, sesame oil, sugar, and water. Mix well and set aside.
Heat a pan with a bit of oil and add the marinated chicken in a single layer. Cook for about 5 minutes, browning on all sides, then remove from the pan and set aside.
In the same pan, add the onions and scallion whites. Cook for a couple of minutes until slightly softened.
Add the chicken back into the pan along with the sauce. Stir continuously until the sauce thickens and coats the chicken and onions.
Finish by adding the scallion greens and cook just until wilted.
Serve over a fresh bowl of rice, or enjoy it straight from the pan.
