Combine all ingredients in a small saucepan and bring to a simmer. Lower the heat to a slow bubble and cook until the rhubarb softens to a mushy texture, about 15 minutes.
Puree the rhubarb with an immersion blender or small food processor until smooth. Refrigerate until cold. Or if you're very thirsty, chill the puree in a bowl of ice water until cold.
Make the cocktail:
Put the strawberries in a cocktail shaker and muddle gently. Add 1 cup of crushed ice and the Rhubarb syrup, lime juice and gin.
Shake vigorously and strain into a glass filled with crushed ice. Top with a splash of sparkling water. Stir once or twice to mix.
To garnish the drink, thread the lime wheels, a slice of strawberry and coiled rhubarb on a cocktail pick.
Keep the rhubarb syrup in a covered container in the refrigerator up to a week. The recipe makes 2 cups, enough for 8 drinks.To make a batch of drinks, multiply the amount of syrup, lime juice and gin into a pitcher and stir. Pour the mixture into ice-filled glasses then top off with a splash of the sparkling water or club soda.