Rinse and scrub the clams and set aside.
Heat the oil in a large wok or Dutch oven set over medium-high heat. When the oil begins to shimmer, add the ginger, garlic, scallions, and red pepper flakes and stir-fry until the garlic begins to color, about 1 minute.
Add the fermented black beans and cook for 15 to 20 seconds, then carefully add the clams to the wok, followed by the rice wine. Cover the wok and allow to cook until the clams begin to open, 5 to 10 minutes, depending on the size of the clams.
Once the clams have started to open, give them a stir in the wok, add the oyster sauce, and stir again. Taste the liquid in the bottom of the wok. If it is not salty enough, add the soy sauce; if it is too salty for you, add the sugar.
Stir in about half of the cornstarch slurry and allow the sauce to thicken. Add more of the slurry if you want a thicker sauce.
Transfer the clams and sauce to a large rimmed platter and sprinkle with the cilantro. Serve immediately.