Preheat oven to 350 degrees F (180 degrees C) and place oven rack to middle position. Butter and flour (or spray with a non stick vegetable/flour spray) the bottom and sides of a 9 x 5 x 3 inch (23 x 13 x 8 cm) loaf pan. Set aside.
Place the nuts on a baking sheet and bake for about 8 to 10 minutes or until lightly toasted. Let cool and then chop coarsely.
In a large bowl combine the flour, sugar, baking powder, baking soda, salt, cinnamon, and nuts. Set aside.
In a medium-sized bowl combine the mashed bananas, eggs, melted butter, and vanilla. With a rubber spatula or wooden spoon, lightly fold the wet ingredients (banana mixture) into the dry ingredients just until combined and the batter is thick and chunky. (The important thing is not to over mix the batter. You do not want it smooth. Over mixing the batter will yield tough, rubbery bread.) Scrape batter into prepared pan. Bake until bread is golden brown and a toothpick inserted in the center comes out clean, about 55 to 60 minutes. Place on a wire rack to cool and then remove the bread from the pan. Serve warm or at room temperature. This bread can be frozen.