Into a small bowl, combine flax meal and hot coffee. It's not enough coffee to create a gel like a "flax egg", but it's enough to soften the flax meal so it's not a noticeable texture in the brownies. Set aside.
Preheat oven to 350ºf F. Line an 8x8 inch baking pan with parchment and set aside.
Add cocoa powder, dark chocolate chips, arrowroot powder, monk fruit sweetener, salt, and baking soda to a food processor, and pulse to break up the chocolate chips until you have a "pebble-like" consistency. Leave some texture to the chocolate.
Into the dry ingredients, add the almond butter, maple syrup, flax mixture, avocado oil, and vanilla. Process until just mixed. If the batter starts to become a ball, it's okay. This is a natural process when nut butter is combined with water.
Stir in walnuts if using.
Bake brownies for 14-16 minutes, until the edges start to pull away from the pan and the tops are glossy.
Allow brownies to fully cool before slicing. Store leftovers in the refrigerator in an air tight container up to a week, or in the freezer up to 5 months.