Place 13×9-inch pan in freezer to chill. Meanwhile, in medium bowl, stir together all ingredients.
Pour into chilled pan; freeze 30 minutes. When ice crystals begin to form at edges of pan, stir mixture with fork. Freeze about 2 hours longer, stirring every 30 minutes, until completely frozen.
Remove granita from freezer 15 minutes before serving. Scrape surface with fork and spoon into individual dessert dishes. Garnish as desired.