Preheat oven to 350°F/175°C. Line a 8x8-inch pan with parchment paper.
In a medium bowl, sift together the cocoa powder, almond flour, oat flour, baking soda, salt, and pumpkin pie spice.
Pour 6 tablespoons of the liquid from a can of chickpeas into a small bowl. With an electric mixer, beat the aquafaba on medium speed until it starts to get foamy, 60-90 seconds.
In a large bowl, beat together the honeynut squash puree, tahini, maple syrup, and coconut sugar until combined. Add in the aquafaba and vanilla and beat until just combined.
Add the dry ingredients to the wet ingredients, and stir to combine with a wooden spoon until smooth and just combined.
Using a silicone spatula, fold in the 1/2 cup dark chocolate chunks.
Add the batter to the prepared baking pan and spread out, smoothing with a spatula. Bake for about 30 minutes, or until a knife inserted in the middle comes out mostly clean and the edges begin to pull slightly away from the pan. Cool the brownies on a wire rack for 20 minutes before adding the ganache.
Make the Chocolate Ganache: Create a double boiler on the stove. Once the water is simmering, add the chopped chocolate and coconut oil, whisking until the chocolate is smooth and melted. Off the heat, stir in the coconut cream and a pinch of sea salt and whisk until well combined.
Spread the ganache over the brownies and top with the 2 tablespoons dark chocolate chunks, chopped hazelnuts, and flaky sea salt. For a firmer brownie, store the brownies in the refrigerator.