1. Place the cucumber, mango, mint, maple syrup, and lime juice in a food processor or blender. Process until fully pureed.
2. Set a fine mesh strainer over a bowl. Pour the mixture into the strainer and let it drip through. Press down on the pulp with a rubber spatula to strain as much liquid out as possible. Whisk in the liqueur.
3. Pour into shot glasses, top with mint sprig, and serve.