Preheat oven to 200°C/180°C fan/400°F (gas mark 6).
In a mini blender or food processor, pulse oats until fine. Add to a bowl with cocoa powder, baking powder, baking soda, and salt. Mix well to combine.
In a separate bowl, whisk together egg, yogurt, sweetener, and vanilla extract until smooth.
Add the wet mixture to the oat mixture and stir until combined.
Spoon the mixture into 9 holes of a doughnut tray. If your tray is not non-stick, grease with spray oil.
Bake for 10 minutes, or until a skewer inserted into the center of a doughnut comes out clean.
Allow doughnuts to cool slightly, then transfer to a rack.
For the glaze:
melt the semisweet chocolate in a bowl by heating it at 10-second intervals, stirring after each interval until melted.
Dip the top of each doughnut into the melted chocolate, then sprinkle with chocolate sprinkles.
