To prepare the simple syrup, add the allulose, water and crushed mint to a small saucepan and heat over medium heat. Stir until the sweetener dissolves completely, approximately 2-3 minutes. Reduce heat to low and simmer for 5 minutes. Remove from heat and strain to remove mint leaves. Set aside to cool.

Add watermelon chunks, fresh lemon juice, and cold water to a blender and blend until smooth. Pour through a strainer to remove any larger particles. Taste and sweeten with the cooled mint-infused keto simple syrup, as desired.

Bruise one-half cup fresh mint leaves with fingers to release oils and add to a large glass pitcher or jar. Top with the watermelon mixture and stir to combine. To serve, pour over ice and garnish with a sprig of fresh mint and a slice of lemon. Enjoy!