Reserve 6 strawberries and set aside. Slice the remaining strawberries and place them in a blender. Sprinkle them with the sugar and stir.
Let the strawberries stand for 20 minutes at room temperature. Then add 1/2 cup of the wine to the blender and blend until strawberries are fully pureed. Pour the mixture through a fine mesh strainer / sieve into a large pitcher and use a spatula to press the strawberry puree through. Discard the seeds.
Add the remaining wine and Grand Marnier to the pitcher. Then add the fresh mint, orange and lemon rounds. Slice the 6 reserved strawberries and add them to pitcher.
Stir and refrigerate the pitcher for at least 1 hour, or up to 4 hours. (Don’t go beyond 4 hours or the fruit texture starts to degrade.)
To serve, pour the sangria into ice-filled glasses and top with a splash of soda water (if desired). Add fruit to each glass, preferably on long skewers for easy snacking.