Preheat your oven to 350°F.

Whisk together the melted butter and brown sugar in a large bowl until well combined. Add in the eggs, mashed bananas, and vanilla, whisking until smooth and creamy.

Combine the dry ingredients by mixing flour, baking soda, salt, and cinnamon in a separate bowl.

Fold the dry mixture into the wet ingredients gently. Stir until just combined, then add in the chopped nuts.

Prepare your muffin cups by greasing or lining them, then divide the batter evenly among the cups. Sprinkle the topping on.

Bake for 14-17 minutes, or until a toothpick inserted comes out clean. Let cool on a wire rack.