Scrub the oysters under cold water with a stiff brush to remove the dirt, especially in the hinge area where mud has a tendency to get trapped. Next, find a durable thick cloth and fold it over several times to create a square; this will steady the oysters as you shuck them and also protect your hand. Using the towel as a mitt, place the oyster, cup-side down in the palm of your towel-covered hand with the hinge facing you; have a small bowl handy to catch the delicious juice. Insert the tip of an oyster knife or dull butter knife as far into the hinge as it will go; don't jab it in there or you could break the shell. With gentle force, twist the knife back and forth to pry the shell open. Using the knife, cut the muscle away from the top shell, bend the shell back, and discard it. Run the knife underneath the oyster to detach it completely, but leave it in its shell. Tip out the briny liquor into the bowl and pour it back over the shucked oysters. Nestle the oysters in a bed of crushed ice or rock salt to keep them steady. Spoon the Cucumber Mignonette on top and serve as part of a raw shellfish bar.
In a small bowl, combine the rice wine vinegar, shallots, ginger, cucumber, black pepper, and cilantro; mixing with a fork. Cover and chill for at least 1 hour or up to the day before you plan to serve, to allow the flavors to come together. Serve with raw oysters and clams.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.