Preheat your oven to 350°F (175°C) and grease a loaf pan.

In a mixing bowl, combine the wet ingredients: eggs, mashed bananas, sugar, oil, and Greek yogurt. Mix until smooth.

In another bowl, whisk together the dry ingredients: whole wheat flour, cornstarch, cinnamon, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

For the crumb topping, mix flour, brown sugar, cinnamon, and butter until crumbly. Sprinkle over the batter in the loaf pan.

Bake in the preheated oven for 60 minutes or until a toothpick inserted comes out clean.

Let the banana bread cool in the pan for 10 minutes before transferring to a wire rack to cool completely.