Slice top and bottom off the watermelon so it sits flat on a cutting board, and has a flat top. Using a large, sharp knife, remove peel and rind.
Lay peeled watermelon on its side and cut into four equal slices. Using a 3-inch (7.5 cm) circular cookie cutter, cut four pieces of watermelon.
To make whipped cream, add cream, icing sugar, and vanilla extract to a tall chilled jar or bowl. Lower in immersion blender and blitz, slowly lifting blender up and down, until whipped cream is thick and creamy.
Top watermelon pieces with a dollop of whipped cream, and garnish with lime zest.