How to Make It
Slice off end pieces of watermelons. Firmly place 1 watermelon at a time on a cutting board; run a knife from top of watermelon to bottom between the flesh and rind. Repeat all the way around until rind has been removed; discard rinds.
Cut watermelon flesh into 3 rectangular blocks: 7- x 5 1/2- x 3-inches, 5- x 3 1/2- x 3-inches, and 3- x 2 1/2- x 3-inches. If your watermelons are on the smaller side, you can reduce the size of the rectangles, just be sure to scale them down evenly, and to cut all blocks to an even thickness.
Place largest block on a cake plate, and insert 2 (6-inch) skewers into center (to secure the tiers); place next biggest block on top. Place smallest block of watermelon on top, creating a tiered cake appearance. Decorate by arranging fruit and mint on all layers of cake (using wooden picks if needed, to help affix fruit). Serve within 4 hours.