Preheat your oven to 350°F. Lightly grease an 8×8-inch square baking dish with coconut oil or cooking spray.
In a small bowl, whisk together the coconut milk, pumpkin puree, melted coconut oil, vanilla extract, and apple cider vinegar until smooth.
In a medium bowl, whisk together the coconut flour, almond flour, erythritol, cinnamon, and baking soda until no lumps remain.
Pour the wet mixture into the dry mixture. Stir with a spatula until the dough starts coming together — it will be thick, more like cookie dough than cake batter. Use clean hands to fully combine and evenly incorporate everything.
Toss in the chopped pecans and mix again with your hands so they’re evenly spread throughout the batter.
Transfer the dough to the prepared baking dish and press it down evenly. Bake for 25 minutes, or until the edges are golden brown.
Remove from the oven and place the pan on a wire rack to cool completely. Frost in the pan if desired, then slice into squares and serve.