Preheat oven to 350 degrees Fahrenheit. Spray a loaf pan and line with parchment paper.
Soak the dates in boiling water for 5-10 minutes to soften. In the meantime, separate your yolks and whites. Put the yolks in a large bowl and the whites in a medium bowl. Beat the egg yolks with an electric mixer (I use handheld) until they become lighter and airier. Then beat the whites with a teaspoon of the maple syrup, until it forms stiff peaks. Set aside.
In a food processor, process the dates and Greek yogurt until smooth. Beat this mixture into the egg yolks until fully combined. Then beat in the mashed bananas, oil, vanilla, and remaining maple syrup.
In a separate bowl, whisk together flour, salt, cinnamon, baking powder, and baking soda. Coat the walnuts in this flour mixture. Whisk the dry ingredients into the wet, then switch to a spatula and fold when it gets too hard to whisk. Fold in the egg whites.
Transfer the batter to the prepared loaf pan and fill until it is ¾ full. If you still have batter left, pour the rest into a mini or regular size muffin tin. Bake the bread for 40-50 minutes, covering for the last 20. Bake mini muffins for about 10 minutes or regular size for 15-20 minutes.
Let the bread cool slightly before serving, about 15-30 minutes.