Place a 9-by-13-inch nonstick metal pan in the freezer.
Stir together the water and sugar until the sugar dissolves. Cut the orange in half. Juice one half and add the juice to the sugar mixture. Peel the other half, being sure to remove all the white pith. Add the orange half to a blender. Add the strawberries and mint to the blender and blend until smooth. Stir in the sugar mixture and pulse one or two more times to combine.
Remove the pan from the freezer and pour in the strawberry mixture. Place it in the freezer. After about 25 minutes, remove the pan and use a fork to scrape the ice crystals from the edges of the pan toward the center. Roughly spread the mixture out and return the pan to the freezer. Repeat 2 or 3 more times, until mixture is all flaky bits of ice crystals. Cover tightly and freeze.
To serve, place in bowls or dessert cups. Garnish with a berry and small mint leaves if desired.