1
Preheat the oven to 350 degrees. Coat a 9" x 9" baking pan with cooking spray and lightly coat with flour.
2
Combine the granulated sugar, bananas, eggs, 1/2 cup of the milk, the oil, and 1 teaspoon of the vanilla extract in a bowl, mixing well. Combine the flour, baking powder, cinnamon, and salt in a separate bowl. Add the flour mixture to the banana mixture and stir until just combined. Fold in the walnuts. Pour the batter into the baking pan.
3
Bake for 28 to 30 minutes, or until a toothpick inserted in the center comes out clean. Cool in the pan for 10 minutes. Turn out of pan onto a rack to cool completely.
4
Meanwhile, combine the confectioners' sugar, remaining 1 tablespoon milk, and remaining 1 teaspoon vanilla extract in a small bowl. Spread the glaze over the banana cake with a small spatula. Cut into 12 squares.