Combine all ingredients except for herbs in a high-speed blender or food processor and blend until smooth. You should have about 3 cups of blended mixture. Pour it into a 8- or 9-inch baking dish and freeze until frozen, at least 4 hours.
Using your hands or a spoon, break the tomato mixture into pieces. Place in a food processor and pulse until slushy. Transfer back to baking dish and freeze until frozen, at least 4 hours.
When ready to serve, process one more time. Scoop into small bowls, garnish with herbs, if desired, and serve.