Trim excess fat from chicken thighs. Heat a tablespoon or so of olive oil in a large, deep skillet over medium-high heat. Add chicken thighs skin side down and cook undisturbed until skin is golden brown, about 7 to 9 minutes. Reduce heat to medium.
Turn chicken, and add garlic and ginger to pan, stirring to spread the aromatics around the pan. Cook, stirring occasionally, for about 4 minutes.
Meanwhile, mix oyster sauce, rice wine, soy sauce, sugar, pepper, cayenne pepper and hot water in a large measuring cup. Add mixture to the skillet (it will spatter pretty well). Cover the pan, reduce heat to medium-low and cook chicken for 15 minutes. Turn chicken, stirring the sauce, then cover pan and cook for another 10 minutes.
Remove lid from pan and raise heat to medium-high. Cook, stirring occasionally, until sauce thickens enough to coat a spatula. (Alternatively, if your sauce has cooked down too much already, stir in a little water. Turn chicken thighs a couple of times to coat with sauce.
Serve with white rice, if desired, spooning sauce over chicken and rice, and sprinkling sliced scallions over all.