1. In a bowl, place the gluten-free buckwheat flour and salt. Gradually pour in the water and mix with a whisk. Add the egg and continue to mix. This will give a nice color to the cooking. Cover the bowl with plastic wrap and refrigerate for at least 1 hour.
2. Meanwhile, prepare the filling.
For the filling, finely chop the garlic and onion. Wash and slice the mushrooms.
In a large skillet, heat the olive oil and sauté the garlic and onion for about 8 minutes. Then add the mushrooms, salt, pepper, and oregano. Let it cook while stirring for an additional 5 minutes. Optionally, deglaze with apple cider vinegar before adding the soy cream. Mix well and let it heat through. Adjust the seasoning to your taste. Coarsely chop the hazelnuts with a good knife and add them to the filling.
3. Your preparation.
Take your galette mixture out of the refrigerator. Grease a crepe pan with a little olive oil using a paper towel and heat over medium/high heat.
Pour a ladleful of batter in the center, quickly swirl the pan to spread the batter evenly. Wait for the galette to brown before using a spatula to lift and flip it. Cook the other side for about 1 minute.
4. Serve the galettes with a generous ladleful of filling in the center, fold the edges, and garnish with parsley.