Start by making the streusel topping. In a mixing bowl, combine ½ cup brown sugar and ¼ tsp salt. Pour the melted butter over this mixture and stir until well combined.
Add 1 cup of flour to the mixture and use a fork to mix until it becomes crumbly. Place the streusel in the fridge while you prepare the banana bread.
In a large mixing bowl, mash the 3 overripe bananas until smooth.
Add the 2 eggs, 1 tsp vanilla extract, 5 tbsp melted butter, ⅓ cup maple syrup, and ½ cup Greek yogurt to the mashed bananas. Whisk everything together until combined.
In another large bowl, mix together the dry ingredients: 1 ¾ cups all-purpose flour, ½ tsp kosher salt, and 1 tsp baking soda.
Gradually add the dry mixture to the wet ingredients, stirring until the flour is almost fully incorporated. Gently fold in the 1 ½ cups of blueberries at the end.
Transfer the batter into a parchment-lined 9x5 loaf pan and sprinkle the prepared streusel topping over the top, gently pressing it into the batter with a spoon.
Bake in a preheated oven at 350°F for 65 to 75 minutes, or until a toothpick inserted into the center comes out with crumbs rather than wet batter.
Once baked, allow the loaf to cool for at least 10 minutes before slicing and serving.
