Preheat the oven to 325˚ F. Line a baking sheet with parchment paper or a silicone baking mat. Place a large skillet over medium heat. Add the chopped hazelnuts and almonds. Cook, stirring occasionally, until lightly browned, 3-4 minutes. Stir in the oats and canola oil and continue to cook, stirring occasionally, until the oats are lightly toasted, about 3 minutes.
Transfer the oat mixture to a large bowl and stir in the honey, espresso powder, ground flaxseed, cinnamon, nutmeg, and salt. Spread out onto the prepared baking sheet in an even layer. Bake, stirring every few minutes, until the granola is light golden brown, about 15 minutes.
Move the granola to one side of the baking sheet and press gently into a thick slab. Let cool to room temperature. Break the dried and cooled granola into small clusters, mix in the chopped chocolate, and store in an airtight container.
*If you prefer a more subtle coffee flavor, use 2 tablespoons of espresso powder. For a more prominent flavor, use 3 tablespoons. Instant coffee powder may also be substituted but you will likely need to use more to achieve the same flavor.