Streusel-Nut Topping: In a small bowl combine 1/4 cup packed brown sugar and 3 tablespoons of flour. Cut in 2 tablespoons of butter until mixture resembles coarse crumbs. Stir in 1/3 cup chopped walnuts and set aside.
Preheat oven to 350F. Grease bottom and sides of a 9x5x3-inch or two 7 1/2x3 1/2x2-inch loaf pans and set aside. In a large bowl, combine flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Make a well in the center and set aside.
In a medium bowl, combine eggs, bananas, sugar, and oil. Add egg mixture all at once to flour mixture. Stir just until moistened (Don't overmix).
Fold in walnuts. Spoon batter into prepared pans. Sprinkle Streusel-Nut Topping over batter in pan(s).
If you are using a 9x5x3-inch pan, bake for 55 minutes to 1 hour. Bake about 40 to 45 minutes for two loaf pans.
Cool in pan on wire rack for 10 minutes, then remove from pan and cool completely. Wrap and store overnight before slicing.