Oysters on the Half Shell with Ceviche Topping

Name: Oysters on the Half Shell with Ceviche Topping
Ingredients: 1 teaspoon coriander seeds; 1/4 cup finely diced peeled Asian pear; 1/4 cup peeled, seeded and finely diced cucumber; 1 serrano chile, seeded and minced; 1 tablespoon minced cilantro; 1 tablespoon fresh lime juice; 1 teaspoon minced candied ginger; 1 teaspoon Asian fish sauce; 1 teaspoon extra-virgin olive oil; Kosher salt; Pepper; 12 freshly shucked oysters on the half shell, such as Rappahannocks