Preheat the oven to 375 degrees F. Line a muffin tin with muffin liners.

In a small bowl, mix together all of the ingredients for the Crumb Topping. Stir together with a fork, and then use your fingers to make it crumbly.

In a large bowl, mix together the flour, baking soda, baking powder, and salt.

In a separate small bowl, mash the bananas (with a potato masher if you have one. If not, a wooden spoon will do). Then beat in the sugar, egg, and melted butter.

Add the banana/sugar/egg/butter mixture to the flour mixture and stir until just combined (do not overmix!)

Fold in the chocolate chips and pecans or walnuts if you are adding them.

Spoon the batter into the muffin tin.

Sprinkle the crumb topping on top of each muffin.

Bake for 22-23 min, or until a toothpick inserted in the center of one comes out clean.

Let cool in the pan on a rack for about 10 minutes, and then transfer the muffins out of the pan, and onto a rack to cool completely.