Preheat oven to 375 degrees and line a baking sheet with parchment paper. In a large bowl combine the flours, coconut, ground flax, granulated maple syrup, baking soda and salt. Chop ½ cup of the walnuts into pieces about the size of chocolate chips and add to flour bowl. In a food processor, carefully pulse the remaining ½ cup of walnuts in short bursts until they resemble a granulated, mealy texture. Be very careful not process the nuts into walnut butter. Transfer ground walnuts into flour bowl and stir to combine. If your coconut oil is solid in texture, gently warm the oil in a small pan on the stovetop until almost liquefied, and remove from heat immediately. In a small bowl, whisk together the coconut oil, liquid maple syrup and vanilla extract until emulsified and set aside to cool slightly. Using a sharp knife, slice down the center of each of the walnut halves and set aside. Pour emulsified liquid mixture into flour bowl and stir until well combined. Using a small ice cream scoop or tablespoon, drop mixture onto parchment-lined baking sheet. You should have about 12 or 13 cookies on the sheet. Shape cookies into mounds and press a sliced walnut into the center of each cookie. Bake for about 10-12 minutes, until lightly golden brown. Remove pan from oven and allow cookies to cool on cookie sheet undisturbed for at least 10 minutes.