Preheat the oven to 350°F (175°C) and line an 8x8-inch pan with parchment paper.
In a food processor, puree the avocados, 1/2 cup maple syrup, vanilla, and instant coffee (if using) until completely smooth.
Add the melted dark chocolate to the avocado mixture and pulse until creamy and combined.
In a medium bowl, whisk the eggs for about 1 minute until slightly bubbly, then stir in the chocolate–avocado mixture until combined.
Sift or add the 1/2 cup cocoa powder, almond meal, and kosher salt to the wet mixture and stir until just combined; fold in the 1/4 cup chopped dark chocolate chunks.
Spread the batter evenly into the prepared pan and bake for 30–35 minutes, until just set; avoid overbaking to keep them fudgy. Let cool completely before frosting.
For the frosting, melt 1/4 cup maple syrup, 1/4 cup coconut oil, and the 2 ounces chopped chocolate together in a small saucepan over low heat until smooth.
Remove the pan from heat and stir in 1/3 cup cocoa powder and a pinch of salt until smooth; let the frosting cool slightly.
Pour or spread the cooled frosting over the cooled brownies in an even layer, then refrigerate for 30 minutes to 1 hour to set.
Once the frosting is set, cut into 16 brownies and serve at room temperature.