01 - Preheat oven to 350°F. Lightly grease a nonstick donut pan.
02 - In a large mixing bowl, whisk mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until fully incorporated and smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Fold the dry mixture gently into the wet ingredients until just combined, ensuring not to overmix.
05 - Transfer batter to a piping bag or resealable plastic bag with the corner snipped and pipe batter into the prepared donut pan, filling each cavity approximately three-quarters full.
06 - Bake for 12 to 15 minutes, or until donuts spring back when lightly pressed and are golden brown.
07 - Remove pan from oven and let donuts cool inside the pan for 5 minutes. Transfer to a wire rack to cool completely.
08 - For the glaze, whisk powdered sugar with milk and vanilla extract until smooth. Dip cooled donuts into the glaze and allow to set for several minutes before serving.