Place strawberries, rhubarb, water, sugar, and juice in blender or 14-cup food processor bowl. Blend on high until smooth. Pour into 9x9-inch glass baking dish. Place in Sub-Zero freezer for 4 hours, stirring with a fork every hour until small pieces of slightly slushy granite are formed. Freeze until ready to serve. Scoop out into frozen martini glasses or smaller frozen bowls. Garnish with fresh strawberries and mint.
To Make Ahead:
Follow above directions and freeze. Thirty minutes before serving, allow granite to rest at room temperature. Then serve as above.