Place the watermelon in a blender and blend until pureed and liquified. Pour the contents through a fine mesh sieve, saving all the watermelon juice in a large pitcher.
Add the sugar, water, ginger and vanilla beans plus the empty pod to a small saucepan. Heat over medium heat while whisking constantly until the sugar dissolves. Allow the mixture to simmer for a minute or two until it becomes syrupy. Remove from the heat and let cool.
To assemble the drinks, add crushed ice in a cup. Pour a few ounces of the vanilla ginger syrup into the cup, then add 4 or so ounces of watermelon juice. Pop the cucumbers in the cub and add about 2 ounces of club soda. Taste and adjust the drink to your desired taste – more syrup or juice, or more club soda. Stir well to mix. Serve!