Preheat oven to 300°F. Line two baking sheets with parchment paper.
In a large bowl, combine the oats, pecans, walnuts, pepitas, sunflower seeds, hemp hearts, ground flaxseed, cacao powder, cinnamon, espresso powder (if using) and salt. Stir until well combined.
Melt the coconut oil. Add the maple syrup and vanilla and whisk together quickly so the coconut oil doesn't begin to firm up again.
Pour the coconut oil mixture over the dry ingredients and stir well until everything is evenly coated.
Divide the granola evenly between the two prepared baking sheets and spread into even layers.
Bake for 20 minutes. Stir the granola on both pans, then return to the oven and bake for another 8-10 minutes, or until dry-looking and fragrant. Baking times may vary slightly by oven.
Let the granola cool completely on the baking sheets. It will continue to crisp as it cools.
If adding dark chocolate, stir it into the granola once completely cooled.