Grind the pecans up in a food processor or blender until a flour forms. Combine the pecan flour, almond flour, rice flour, oat flour, coconut sugar, ground flaxseed and baking soda in a bowl. Add the chunks of butter to the flour and use a pastry blender or the back of a fork to work the butter into the flour. Once a crumbly dough forms, add the cold water ½ tablespoon at a time until a uniform dough forms. If the dough is still crumbly after 2 tablespoons, add more water 1 teaspoon at a time.
Preheat your oven to 325 degrees. Grease a pie pan and press the dough into the pan. Take your time forming the crust so it is of uniform thickness and has whatever type of design you’d like for the sides. Poke a few holes into the bottom of the crust using a fork. Prebake the crust for 12 minutes, then set it aside.
In a saucepan or small pot, melt the butter for the filling over medium heat. Once the butter begins to melt, add the coconut sugar. Whisk until the coconut sugar melts and then add in the maple syrup, coconut milk and vanilla extract. Whisk until combined and let the mixture come to a boil. Reduce the heat so that the liquid is gently boiling. Continue boiling the filling until the mixture reads 230 degrees on an instant-read thermometer. Give the mixture a whisk and set it aside to cool. If you are adding the cinnamon add it now.
Once the mixture has cooled and is still a little warm, Whisk the three eggs together well. Slowly ladle the mixture into the eggs, whisking as you go until everything is well combined. Pour the filling into the prebaked pie crust. Place the pecan halves on top of the filling in whatever pattern you’d like. The pecans may sink slightly into the filling but that’s okay. Bake the pie for 25 minutes or until the center is just set. Allow the pie to fully cool, then transfer the pie to the oven for an hour or so before slicing and serving.