Preheat the oven to 325ºF (165ºC). Line the bottom a 9 x 5-inch loaf pan* with parchment paper. Grease and flour the insides.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon and nutmeg until well blended.
In a large bowl, whisk together the brown sugar, oil, eggs, sour cream and vanilla until creamy and well blended. Stir in the bananas until incorporated. Mix in the flour mixture just until combined. Do not over mix. Stir in the pecans.
In a small bowl, gently toss the blueberries with the lemon juice, then toss them with 2 teaspoons of flour. Fold 3/4 of the blueberries into the batter. Transfer the batter to the prepared loaf pan. Top with the remaining blueberries, then the crumb topping.
Bake until a toothpick inserted into the center of the loaf comes out clean, about 55-60 minutes. Cool in the pan for 10 minutes, then remove the loaf from the pan and transfer to a cooling rack to cool completely.