Preheat oven to 375°F. Line a 9-inch square pan with parchment paper.
In the bowl of a food processor, combine the millet flour, oat flour, sweet rice flour, tapioca starch, xanthan gum, sea salt, baking powder and Monkfruit granulated sweetener by pulsing a few times.
Add the vanilla and butter and pulse until a crumbly dough forms.
Transfer the dough to the parchment paper lined pan and press firmly to form the base.
Bake for 15 - 18 minutes or until it begins to turn golden brown. Remove from oven and let cool for 10 - 15 minutes.
Wash the food processor bowl, add the eggs and tapioca starch and process until well combined. Add the Lacanto maple-flavoured syrup, coconut sugar, melted butter and vanilla and process until well combined. Add the walnuts and pulse until coarsely chopped.
Pour the filling on to the cooled base. Spread evenly.
Bake for 20-24 minutes or until completely set. Cool completely before slicing.