a 10-inch round tart pan with 2-inch sides and removable bottom
For the dark chocolate graham cracker crust: Break the chocolate into pieces and place in the bowl of a food processor along with the graham cracker crumbs. Blend together until combined. Cut the stick of butter into several pieces and add to the food processor. Blend again until the mixture starts to clump together and has the consistency of wet sand.
Dump the crumb mixture into a 10-inch round deep tart pan with 2-inch sides and a removable bottom. Press the crumbs into the bottom and towards the sides of the pan using the bottom of a glass. Then press down from the top with your thumb along the lip of the crust and press against the wall of the crust to create a scalloped edge. Gently scrape away the inside of the tart walls with a spoon while still pressing down from the top so that the crust is consistently 1/2-inch to 2/3-inch thick all the way around. Press and smooth the crumbs across the bottom of the pan. Refrigerate the crust for about 1 hour.
For the strawberry smoothie mousse filling: Sprinkle the gelatin over the coconut milk in a medium microwave-safe bowl and let sit 1 minute. Microwave on high for 40 seconds, then stir until the gelatin is completely dissolved.
Pulse the strawberries, 1 tablespoon sugar and the coconut gelatin mixture in a food processor or blender until the berries are pureed. Add the cream cheese, Greek yogurt and vanilla extract and continue blending until smooth. Taste and add another tablespoon of sugar if desired, then scrape down the sides and blend again. Pour into the prepared crust and refrigerate for 2 hours.
For the decorative topping: Gently push the strawberries decoratively into the semi-gelled filling, then press in the blueberries, blackberries and raspberries to make a pretty pattern. Sprinkle the hazelnuts over the surface. Refrigerate until set, 4 to 6 more hours or overnight.
To unmold the pie, carefully press up from the bottom of the tart pan, then slice with a sharp knife (the crust will be very firm) and serve.