Prepare the crust: In a food processor combine almond flour, tapioca flour, salt and cold butter and pulse until the butter is broken down into pea-sized pieces. Add in egg and honey and process until the dough comes together. Shape dough into one round disk, wrap tightly in plastic wrap and transfer to refrigerator until cold, at least 4 hours or overnight.
Prepare the filling: Mix the strawberries, rhubarb, lemon juice, sugar, arrowroot starch, and vanilla together in a large bowl. Cover and refrigerate until the dough is ready.
Preheat oven to 350 degrees.
Once dough is chilled and oven is preheated, between two sheets of parchment or plastic wrap, roll out dough to about a 12 inch circle. Move dough onto parchment lined baking sheet.
Spoon the strawberry rhubarb filling (not the juices) into the center of the dough, leaving a 2-3 inch border all around. Gently fold the edges of the dough over the fruit, overlapping the dough as necessary. Press gently to seal the edges.
Brush the edges of the galette with egg wash and sprinkle with coconut sugar.
Bake the galette for 35-40 minutes until the edges are golden brown.
Remove from the oven, let sit about 15-20 minutes before slicing and serving.