In a small pot, cook the rhubarb with the brown sugar, the water, and about half of the strawberries for about 3-5 minutes on high heat. After cooking, add the orange juice and either use an immersion blender or transfer it to your blender to puree it. Let it cool down for a bit.
Add 3 tablespoons of the rhubarb puree to each glass and evenly divide the sparkling wine.
Serve the rhubarb cocktail with fresh strawberries, orange slices, mint leaves, and ice cubes. Enjoy!