Make the crust:
In a bowl, combine graham cracker crumbs, sugar, cocoa powder, and melted butter. Mix well until crumbly and fully combined. Press the mixture evenly into the bottom of a 9×11-inch baking dish to form a smooth crust. Cover with plastic wrap and refrigerate for about 30 minutes to set.

Prepare the filling:
In a large bowl, blend together the cream cheese and mascarpone until smooth. Stir in the lemon zest, lemon juice, and vanilla extract until evenly mixed.

Whip the cream:
In a separate chilled bowl, whisk the heavy cream and sugar until soft peaks form. Gently fold the whipped cream into the cheese mixture until the filling is light, fluffy, and fully combined.

Assemble the cheesecake:
Spread the filling evenly over the chilled crust, smoothing the top with a spatula. Tap the dish gently on the counter to settle the layers. Cover tightly with plastic wrap and refrigerate for at least 3 hours, until set.

Decorate with berries:
Starting along the bottom long edge, arrange a horizontal line of strawberry halves with the pointed ends facing right. Create a shorter line near the top right corner for the top stripes. Continue layering 3 more full-length strawberry stripes about ¾ inch apart, leaving space for a square “blue” field in the upper left corner.

Fill this square space with rows of blueberries, placing them closely together with the blossom ends facing up.

Serve:
Slice into squares and enjoy your festive, no-bake cheesecake!