In the bowl of a food processor, place dates, cashews, oats, and salt. Process until "dough" comes together and cashews are in small pieces. If your mixture is not coming together, add a teaspoon of water.
Press mixture into the bottom of prepared pan into an even layer. In a small bowl add melted coconut oil, cocoa powder, and maple syrup. Stir until cocoa powder is dissolved. Pour chocolate mixture over the nut mixture in the pan. Use the back of a spoon to spread into an even layer. Press blackberries on top of chocolate layer until covered. Refrigerate for at least 25 minutes or until chocolate has set.
Using the parchment as handles, remove from pan. Slice with a sharp knife into squares. Store in an airtight container in the refrigerator.