Preheat the oven to 350°F (180°C). Spray two 8 inch cake pans with non-stick spray and line the bottoms with circles of parchment paper. Set aside.
Sift the flour and cocoa powder into a mixing bowl and then add the sugar, baking soda and salt and mix together.
Prepare your flax egg by adding 1 and ½ Tbsp ground flaxseed meal to a bowl and then adding in 4 and ½ Tbsp hot water (this equals 1 and ½ flax eggs). Leave it to sit for a minute and become gloopy.
Add in the soy milk, vanilla extract, oil, vinegar and flax eggs to your dry ingredients and mix in. Use a hand whisk to briefly mix it all together removing any lumps (tiny lumps are fine) but being careful not to overmix.
Divide the batter evenly between the two cake pans and then place into the oven to bake for 30 minutes or until a toothpick inserted into the center of one of the cakes comes out clean. Transfer the cakes to a wire cooling rack to cool completely before adding filling or frosting.
While the cakes are baking, prepare your coconut pecan filling. Mix the cornstarch into the cold coconut milk and whisk so that it's well mixed in. Then add the vegan butter to a saucepan and let it melt before you add the brown sugar and coconut milk/cornstarch mix. Stir constantly until the mixture boils and starts to thicken, then remove it from the heat and add in the vanilla, coconut flakes and chopped pecans. Set aside to cool completely before using.
Prepare your chocolate buttercream frosting. Add the powdered sugar, cocoa powder, vegan butter, 3 Tbsp of coconut milk and vanilla extract to the bowl of an electric stand mixer. Start off at slow speed, gradually increasing speed until it's very thick and smooth. If needed, add in extra coconut milk a tiny bit at a time to get to the ideal consistency.
When the cakes are completely cool and your coconut/pecan filling is completely cold, then you can finalize your cake. Add all the coconut/pecan filling to the middle layer and then all the chocolate buttercream to the top. If you want to frost the sides as well you can do that, there is enough frosting to allow for this.
Decorate the cake with coconut flakes, chopped pecans and vegan chocolate chips (optional).