Preheat the oven to 175C/346F. Grease a 9' round baking pan with coconut oil and set aside.
Add the chopped chocolate and coconut oil into a heatproof bowl and place over a pot with simmering water. Turn the heat to low and let the chocolate melt, stirring frequently, to incorporate the coconut oil. When the chocolate is completely melted, remove the bowl from the pot and set aside.
Beat the eggs into a large bowl.
Add the walnuts into the food processor and pulse a few times to obtain a fine flour. Add Save 1 tablespoon for garnishing, then add the cocoa powder and salt, pulse one more time to incorporate and transfer into the bowl with the eggs.
Slowly add ⅔ of the melted chocolate coconut mixture to the egg bowl, mixing constantly, to incorporate. Save the ⅓ left for garnishing the cake.
Pour the mixture into the baking pan and bake for 30 minutes, until set.
Remove from the oven and let cool completely before removing from the pan.
Pour the rest of the melted chocolate mixture on top of the cake, and garnish with walnut flour and coconut flakes. Cut into slices and serve.