Preheat your oven to 350 degrees Fahrenheit.
Grease your loaf pan with a thin layer or spray of vegetable oil and then line it with parchment paper. Set aside.
In the bowl of a stand mixer whisk together the flour, sugar, cocoa powder (1/3 cup only), baking soda, salt and vanilla powder (if that is what you are using). Whisk together to combine well.
Next add to the flour mixture the vegetable oil, vinegar and water (and if you are using vanilla extract, add that in now).
Using the paddle attachment of your stand mixer, mix all of the ingredients together until well combined.
Toss your frozen blueberries with the 1 tablespoon of reserved cocoa powder until well coated.
Gently fold the blueberries into your cake batter using a rubber spatula.
Pour your batter into the prepared loaf pan. Smooth out the top with your rubber spatula.
Bake your cake in the middle rack of your oven for 55 - 60 minutes or until a toothpick inserted into the center of your cake comes out clean.
When your cake is ready, allow it to cool for 5 minutes in the loaf pan until transferring it out onto a cooling rack.
Once your cake is completely cooled, prepare your glaze. Melt the chocolate chips and coconut oil using a double boiler and once melted and smooth, pour the glaze over the loaf pan.
Decorate the top of your cake with fresh blueberries if desired.