Preheat the oven to 180°C and place waxed paper on a baking sheet.
In a large bowl, combine the oat flour, whole wheat flour, almond flour, baking powder and pinch of salt. Mix well.
Add the coconut oil, Greek yogurt and sweetener to taste. Mix well with a spatula or your hands.
Incorporate the 2 eggs one at a time, mixing well after each addition. Add the oat milk little by little, kneading until you obtain a uniform and manageable dough.
On a lightly floured surface, roll out the dough with a rolling pin to form a rectangle about 1 cm thick.
Cut the dough into triangles. Roll each triangle from the base towards the vertex, forming a croissant. Fold the ends inward to give them the classic half-moon shape.
Transfer the croissants to the baking sheet, leaving space between them.
Beat the remaining egg and use a brush to brush over the top of the croissants, ensuring a golden finish.
Bake for 15-20 minutes, or until the croissants are golden brown and firm to the touch.