1. Preheat oven to 350oF.
2. Line an 8x8 inch pan with parchment paper so that you're able to easily remove the bars after. This is important! Grease the parchment paper with nonstick cooking spray.
3. Prepare the filling first: Add dates, hot water, and espresso powder to a food processor or high-powered blender and blend until smooth, about 2 minutes.
4. Allow date mixture to cool and thicken for 5 minutes while you make the base.
5. To make the oat base (and crumble): In a large bowl, combine oat flour, oats, baking soda, brown sugar, cinnamon, salt, and vanilla.
6. Stir in melted coconut oil until the mixture is crumbly. Measure out 1 cup of the mixture and set aside in a small bowl (this will be for the topping).
7. Press the remaining mixture into the prepared pan; you'll need to press hard to ensure that all of the mixture will stick together well.
8. Next spread date mixture evenly on top of the base crust.
9. Sprinkle on chopped dark chocolate then sprinkle the reserved oat topping over the top.
10. Bake for 30-35 minutes or until top is set and slightly golden brown.
11. Transfer to wire rack to cool for at least an hour, and then remove from pan to cool completely.