Place the cubed watermelon in a freezer container and freeze. Just before serving, combine the frozen watermelon, strawberries, rosé and mint in a blender. Secure the lid and blend until smooth. Serve immediately, garnished with a sprig of mint.
For a non-alcoholic version, use a non-alcoholic rose or substitute it with apple juice, white grape juice, ginger ale or coconut water with a squeeze of lime.