Add raspberries, lemon juice, Grand Marnier, rum, ginger powder, sugar and ice into a blender. Purée until smooth.
Pour the purée into a pitcher. Pour the soda water over top and stir gently to combine.
Gently muddle a few mint leaves at the bottom of each glass. Pour the beverage into glasses over top of the muddled mint. Add more mint leaves and ice, if desired and a twist of lemon peel to garnish.
Serve and enjoy!
Notes
If you like, you can put the blended ingredients through a strainer to get rid of all of the seeds from the raspberries. I personally like the crunch.