Preheat oven to 350°F and line a baking sheet with parchment paper.
In a small bowl, combine slightly warmed Greek yogurt, honey, and active dry yeast; let it sit for 5-8 minutes until bubbly.
Whisk the egg whites into the yogurt mixture until smooth and aerated.
In a separate bowl, stir together oat flour, protein powder, sea salt, and cinnamon.
Gradually fold the dry ingredients into the wet mixture until a soft, pliable dough forms.
Divide the dough into four equal pieces, roll each into a long log, and pinch the ends together to create a donut shape.
Place the donuts on the prepared baking sheet, cover with a clean towel, and let rise in a warm spot for 30 minutes.
Bake for 12-15 minutes until the donuts are puffed and lightly golden.
In a small ramekin, whisk together the maple syrup and melted coconut oil to create a thin glaze.
Dip the tops of the warm donuts into the glaze and let them set for 2 minutes before serving.