Preheat your oven as per the instructions on the cake mix box. Prepare your cake batter as instructed, and bake in a round cake pan. Allow it to cool completely.

In a medium saucepan, combine the strawberries, sugar, and lemon juice. Cook over medium heat until the strawberries have softened, about 5-7 minutes. Puree the mixture using a blender and allow it to cool slightly.

In a small bowl, sprinkle the gelatin over the cold water. Let it sit for about 5 minutes until it blooms. Then, heat it briefly in the microwave or over low heat until it dissolves completely.

In a mixing bowl, whip the heavy cream until soft peaks form. Slowly fold in the strawberry puree and the dissolved gelatin until evenly mixed.

Once the cake has cooled, slice it in half horizontally. Place the bottom layer on a serving platter and spread a generous layer of strawberry mousse over it. Place the top layer of the cake back on top.

In a small saucepan, combine the chocolate chips and butter over low heat. Stir until melted and smooth. Let it cool slightly, then pour over the top of the cake, letting it drizzle down the sides.

Decorate the top of the cake with whole or halved fresh strawberries. If desired, drizzle with extra melted chocolate for an added touch.

Refrigerate the cake for at least 2 hours to set the mousse before serving.