Place the rhubarb, sugar, water and and citrus peel in a small pan. Bring to a simmer and cook until the rhubarb becomes very soft, 12-15 minutes.
Pour the mixture through a strainer set over a bowl to let the syrup run through. Stir gently to expedite the process, but try not to push too hard or the solids will cloud the syrup. Cool before using. Refrigerate for a up to week or two.
Mix the drink:
Combine ingredients for cocktail in a shaker with ice cubes. Shake vigorously and strain into a rocks glass filled with crushed ice. Garnish with lime wheel.
The rhubarb syrup recipe will yield more than enough for 4 drinks. Double the batch for a party.
Stir extra syrup into sparkling water for a non-alcoholic cocktail or pour over fresh strawberries and yogurt.
If you prefer, switch out the gin for tequila or vodka.