Preheat the oven to 350 degrees F and lightly oil or spray a 13" x 9" baking pan (or 10-inch round cake pan).

Mash up the bananas in a mixing bowl until smooth. Whisk in the eggs, pure maple syrup, and vanilla extract.

In a separate bowl, stir together the dry ingredients (including the chocolate chips and walnuts). Add the dry mixture to the wet and stir well.

Transfer the cake batter to the prepared cake pan. Bake on the center rack of the oven 55 to 65 minutes, until golden-brown around the edges. Remove from the oven and sprinkle with sea salt if desired.

Allow cake to cool at least 30 minutes before cutting and serving.