Preheat the oven to 180°C (356°F).
In a bowl, mix together the protein powder, almond flour, cocoa powder, baking powder, and salt.
In another bowl, mash the banana and mix in the egg, almond milk, and honey until well combined.
Combine the dry ingredients with the wet ingredients and mix until smooth.
Add dark chocolate and nuts and gently fold them in.
Pour the batter into a baking pan.
Bake in the oven for 20-25 minutes.
Let it cool completely, then cut into serving-sized pieces.