Puree tomatoes and juice, vodka, hot sauce, lemon juice, salt, peppers, Worcestershire sauce, and 250ml water in a blender.
Pour into a freezable dish.
Chill in freezer, scraping every 30 minutes with fork, until frozen, 2 to 3 hours.
Shuck oysters, leaving them on the half shell.
Arrange on a bed of crushed ice.
Top each with 1 teaspoon granita, and serve immediately