To prepare mignonette, mix ginger, shallot, pepper, soy sauce, vinegar, and yuzu juice in a small bowl and let stand for flavors to blend, about 20 minutes.
Meanwhile, in a separate bowl, toss cucumber, pear, and chives.
To serve, arrange oysters on a platter of crushed ice, drizzle each with a teaspoon of mignonette, and top with a spoonful of the cucumber-pear mixture.
Garnish with tobiko.