Slice the bottom of the lemon and 1/3rd of the top off. Use a pairing knife to slice the flesh away from the pith. Scoop out the lemon flesh with a melon baller or a spoon. Place rinse the lemons out with water and place them in the freezer.
Heat up water and monk fruit crystals in a small sauce pan. Allow mixture to simmer util the crystals dissolve. Add the lemon zest to the simple syrup and allow it to rest until it cools to room temperature.
Transfer the lemon flesh to a nut milk bag and squeeze the juice out. Discard the pulp. Combine the lemon juice with the simple syrup. Strain the zest out of the syrup.
Place the mixture into a freezer safe container and allow to freeze for 4 hours. Transfer mixture to a food processor to churn. Spoon the churned lemon zest into the lemons and garnish with a mint leaf. Return to the freezer prior to serving.