In a medium bowl, whisk together the flour, granulated sugar, brown sugar, and cinnamon for the crumb topping.

Add the cold, cubed butter to the dry ingredients. Use your fingertips or a pastry blender to cut the butter into the flour mixture until coarse crumbs form.

Place the bowl in the refrigerator while you prepare the banana bread batter.

Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan, or line with parchment paper leaving an overhang on the sides for easy removal.

In a large bowl, mash the very ripe bananas using a fork or potato masher until mostly smooth with a few small lumps remaining.

To the mashed bananas, add the melted butter, granulated sugar, brown sugar, eggs, and vanilla extract. Whisk until well combined.

In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt until thoroughly combined.

Gradually add the dry ingredients to the wet ingredients, mixing with a spatula until just combined. Be careful not to overmix; a few streaks of flour are okay.

Gently fold in the diced fresh strawberries until evenly distributed throughout the batter.

Pour the banana bread batter into the prepared loaf pan.

Retrieve the crumb topping from the refrigerator and generously sprinkle it over the top of the banana bread batter in the pan.

Bake for 55-65 minutes, or until a wooden skewer or toothpick inserted into the center of the loaf comes out clean. If the topping starts to brown too quickly, you can loosely tent the loaf with aluminum foil.

Remove the loaf pan from the oven and let the bread cool in the pan for 15-20 minutes before carefully lifting it out onto a wire rack to cool completely.

Slice and serve warm or at room temperature.