Place the watermelon on a clean cutting surface and use a sharp knife to slice off both ends. Then, cut the watermelon into thick, even discs about 2-3 inches thick.
Using a spoon or melon baller, carefully carve out the inner flesh of the watermelon discs, leaving a solid outer ring to resemble a cake layer. Repeat for each disc, ensuring the edges remain even and intact.
Stack the carved watermelon discs on a serving platter, aligning the layers to create a tiered cake shape. Optional: drizzle lime juice over the layers and garnish with fresh mint leaves for added flavor and visual appeal.
Chill the assembled watermelon cake in the refrigerator for at least 30 minutes to enhance the crunchiness and keep it cold before serving.
Just before serving, optionally add extra mint leaves or lime zest on top. Slice into wedges with a sharp knife, revealing the layered, vibrant red interior of the carved watermelon slices.