Preheat oven to 425 F and line a 12 cup standard muffin tin with paper liners.
Mix streusel ingredients until sandy. Set aside while you make muffins.
In a mixing bowl, whisk dry ingredients (flour, kinako, baking powder, baking soda, salt, and cinnamon). Set aside.
In a separate bowl, mash bananas and mix with brown sugar, melted butter, eggs, and vanilla.
Mix the dry ingredients with the wet ingredients.
Divide the batter into the 12 muffin liners. It should fill the cups all the way to the top. Sprinkle the streusel on top (you may have extra).
Bake for five minutes at 425F. Then, without opening the oven, reduce the temperature to 350F and bake for another 15 minutes or until a toothpick inserted in the center comes out clean.
Store leftovers in an airtight container. It's fine at room temperature or you can keep in the refrigerator if your kitchen is hot and humid.
Notes
For the optional streusel, you can substitute half flour for the kinako if you'd like a milder flavor.
You can substitute all purpose flour for the whole wheat flour as well.