Thaw the frozen riced cauliflower completely. Place in a clean kitchen towel or several layers of paper towels and squeeze firmly to remove as much moisture as possible.

Add gluten-free flour, sugar, salt, drained cauliflower, and cold butter cubes to a food processor. Pulse until the butter is pea-sized and the cauliflower is well incorporated into the flour mixture.

With the processor running, slowly drizzle in cold water 1 tablespoon at a time. Stop adding water as soon as the dough begins to come together and forms a rough ball. You may only need ¼ cup of water.

Turn the dough onto a lightly floured surface and gently work into a disk shape. Wrap tightly in plastic wrap and refrigerate for at least 2 hours.

In a medium bowl, combine sliced strawberries, honey, cinnamon, lemon juice, cornstarch, and salt. Toss gently to coat the strawberries evenly. Set aside while the crust chills.

Remove the chilled dough from the refrigerator and place on a large piece of parchment paper. Roll out the dough to ⅛ to ¼ inch thickness, forming a rough 12-inch circle. Use your hands to gently patch any cracks that form.

Brush the entire surface of the pie crust with the beaten egg white. This creates a barrier to prevent a soggy bottom.

Arrange the strawberry mixture in the center of the crust, leaving about 3 inches of border around the edges.

Working around the circle, gently fold the edges of the crust up and over the strawberry filling, overlapping slightly as you go. The center should remain open, and rustic pleats are perfectly fine.

Brush the folded edges with more beaten egg white and sprinkle with granulated sugar if desired.

Carefully lift the parchment paper with the assembled galette and transfer to the prepared baking sheet.