Preheat oven to 350 degrees F. Grease 12 muffin cups.
In a food processor, process beans with 1-2 tablespoons of water to make a puree. Add bananas, eggs, brown sugar, yogurt, oil and vanilla. Puree until smooth.
In a large bowl, whisk together the flour, baking powder, baking soda, cinnamon and ginger (if using). Add salt if desired.
Add the wet ingredients to the dry ingredients and mix to make a thick batter.
Fold in nuts and/or chocolate chips.
Spoon batter into muffin cups and put in the oven.
Bake for 20 to 25 minutes or until a toothpick inserted comes out with moist crumbs.