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 mixture and add more sugar or lime juice as needed to achieve desired sweetness and tartness balance.
04 - Pour the pureed mixture into the prepared pan. Tap the pan gently on the counter to release air bubbles and create an even surface.
05 - Place pan in freezer for 4 hours or overnight until completely firm and set.
06 - Lift the frozen block from the pan using parchment overhang. Cut into 12 equal rectangles with a sharp knife, running under warm water if necessary for clean cuts.
07 - Garnish with fresh chopped mint and lime wedges immediately before serving. Serve directly from freezer.