For the frosting: With an electric mixer, beat the heavy cream, sugar and vanilla on medium-high speed until the cream reaches stiff peaks. Refrigerate until ready to use.
For the cake: Cut off the ends of the watermelon, leaving the middle section; remove the rind. Pat the outside of the watermelon dry with paper towels. Set the "cake" on a serving plate.
Cover the watermelon cake with the frosting. Press the almonds into the sides of the cake. Top with the strawberry slices. Cut into 6 to 8 wedges and serve immediately.