Combine sugar, water, vanilla pod and seeds, and rhubarb in a medium saucepan and bring to a boil, stirring to dissolve sugar. Simmer until rhubarb is tender, about 3 minutes. Let cool completely. Pour the syrup through a sieve, discarding the rhubarb. Remove vanilla pod before serving, if desired. Syrup (with vanilla pod) can be stored in refrigerator up to 1 week.

Combine gin, syrup, and lemon juice in a pitcher and stir to combine. Divide among ice-filled glasses and top off each with 2 ounces wine. Stir gently and garnish with lemon rounds. Serve immediately.

Alternatively, you could do a non-alcoholic drink option with replacing gin and Prosecco with sparkling water.