01 - Preheat oven to 350°F. Lightly grease a donut pan with oil or nonstick spray.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon until well blended.
03 - In a large bowl, beat the sugar, eggs, Greek yogurt, oil, and vanilla extract until smooth and thoroughly combined.
04 - Gradually add the dry ingredients to the wet mixture, stirring gently until just incorporated. Avoid overmixing to prevent tough donuts.
05 - Transfer batter to a piping bag or zip-top bag with corner snipped. Pipe evenly into donut pan, filling each cavity about 2/3 full.
06 - Bake for 10-12 minutes until lightly golden and a toothpick inserted into the center comes out clean.
07 - Let donuts rest in the pan for 5 minutes, then carefully remove and transfer to a wire rack to cool completely.
08 - Whisk together powdered sugar, milk, and vanilla until smooth. Dip cooled donuts into glaze and place on rack to set.