Mix about 2 TBSPP of flour with the blueberries and keep it ready.
Sift the flour along with baking soda, baking powder and salt.
Peel the bananas and place it in a bowl
Mash the bananas well with a fork.
Add vanilla and mix.
Pour oil and mix.
Add sugar and whisk well.
Add the sifted flour mixture.
Mix gently with a spatula until just combined. Do not over mix.
Add the blueberries saving a few to place on top of muffin.
Place liners in a muffin tin (optional) and fill it with batter.
Evenly distribute the reserved blueberries on top of the batter.
Pre-heat the oven to 350 F.
Sprinkle the crumb topping on top of the batter.
Bake for 20 to 22 minutes or until the toothpick comes out clean.