Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.

In a medium bowl, combine 1/2 cup all-purpose flour, 1/3 cup light brown sugar, and 1 teaspoon ground cinnamon. Mix with 1/4 cup melted unsalted butter until crumbly.

In another bowl, whisk together 2 cups all-purpose flour, 1 teaspoon baking soda, 1/2 teaspoon salt, and 1 teaspoon ground cinnamon.

In a large bowl, mash 3 ripe bananas, then stir in 1/2 cup granulated sugar, 1/4 cup melted unsalted butter, 2 large eggs, and 1 teaspoon vanilla extract until blended.

Gently fold the dry ingredient mixture into the wet ingredients until just combined, being careful to not overmix.

Pour half of the batter into the prepared pan, sprinkle half of the cinnamon-sugar swirl mixture over, followed by the remaining batter and finally the rest of the swirl on top.

Sprinkle the streusel topping evenly over the batter in the loaf pan.

Bake in the preheated oven for 50-60 minutes or until a toothpick comes out clean.

Cool in the pan for 10 minutes, then turn onto a wire rack to cool completely.