To prepare granita, place first 4 ingredients in a blender or food processor; process until smooth. Place tomato mixture in an 8-inch square baking dish; cover and freeze until firm, stirring twice during the first 2 hours. Remove mixture from freezer; scrape entire mixture with a fork until fluffy.
To prepare salad, divide tomato slices evenly among 6 plates. Sprinkle tomatoes evenly with pepper and 1/4 teaspoon salt. Top each serving with 2 tablespoons granita. Sprinkle with basil leaves, if desired.
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov.