01 - Preheat oven to 350°F. Lightly grease a standard 12-cavity donut pan with oil or non-stick spray.
02 - In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, ground cinnamon, and salt until evenly distributed.
03 - In a separate bowl, combine the mashed bananas, eggs, vegetable oil, milk, and vanilla extract. Whisk until smooth and well blended.
04 - Pour the wet mixture into the dry ingredients and fold gently with a spatula until just combined. Avoid overmixing to keep the donuts tender.
05 - Spoon or pipe the batter into each donut cavity, filling approximately three-quarters full to allow room for rising.
06 - Bake for 12 to 15 minutes, or until the donuts spring back when lightly pressed and a toothpick inserted into the center comes out clean.
07 - Let the donuts rest in the pan for 5 minutes, then transfer to a wire rack to cool completely before glazing.
08 - Whisk together powdered sugar, milk, and ground cinnamon until smooth. Drizzle over the cooled donuts and allow the glaze to set before serving.