Preheat oven to 425 degrees. Line muffin tin with cupcake liners.
In a large bowl, combine flour, baking powder, baking soda, cinnamon and salt.
In a medium bowl, whisk together the melted butter, eggs, both sugars, milk and vanilla. Mix in the mashed bananas.
Pour the wet ingredients into the dry ingredients. Mix until all the dry ingredients are incorporated. Do not overmix.
Add in the chopped pecans.
Divide evenly amongst the 12 cupcake liners.
Topping
In a small bowl, combine sugar, flour and butter. Use your fingers or a fork to break apart the butter. Stir in oats and pecans.
Sprinkle topping over divided muffins.
Bake for 5 minutes at 425 degrees, then lower the oven temp to 375 degrees and bake for an additional 12-15 minutes, or until a toothpick inserted comes out clean.
Allow to cool in pan 5 minutes, then remove to wire rack to cool complete.
Notes
Baking the muffins at an initial high temperature makes them rise quickly, leading to the bakery-style muffin tops. Store in airtight container at room temp for up to 3 days.