01 - Preheat the oven to 350°F. Lightly grease a nonstick donut pan.
02 - In a large mixing bowl, whisk together the mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until fully blended.
03 - In a separate bowl, sift together the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry ingredients into the wet mixture until just combined. Avoid overmixing for optimal texture.
05 - Transfer batter to a piping bag or a resealable plastic bag with a snipped corner, and pipe into the prepared donut pan, filling each cavity about three-quarters full.
06 - Bake for 12 to 15 minutes, or until donuts are golden and tops spring back when lightly pressed.
07 - Remove pan from oven and cool donuts in the pan for 5 minutes. Transfer donuts to a wire rack to cool completely before glazing.
08 - For the glaze, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze and set back on the rack for a few minutes to allow the glaze to firm.