01 - Line an 8x8-inch baking pan with parchment paper, allowing overhang on all sides for easy removal of the frozen bars.
02 - Combine watermelon cubes, lime juice, lime zest, and sugar in a blender. Process until completely smooth and no fruit chunks remain.
03 - Taste the puree and adjust sweetness or lime intensity according to personal preference before proceeding.
04 - Transfer the mixture to the prepared pan. Tap the pan gently on the counter to release air bubbles and create an even surface.
05 - Place the pan in the freezer for approximately 4 hours, or until the mixture is completely solid and can be cut cleanly.
06 - Lift the frozen block from the pan using the parchment paper overhang. Use a sharp knife to cut into 12 equal bars, running the knife under hot water between cuts if necessary.
07 - Top bars with freshly chopped mint and lime wedges immediately before serving, if desired. Serve directly from the freezer for best texture.