1 teaspoon pure vanilla extract
Position a rack in the center of the oven and preheat the oven to 350°F. Spray a 9x5x3-inch loaf pan with nonstick cooking spray.
Spread 1½ cups of the walnuts on a large heavy baking sheet. Bake, stirring occasionally, for about 8 minutes, or until the walnuts are toasted and a nut broken in half is golden brown in the center. Let cool, then coarsely chop.
In a medium bowl, whisk the flour, baking soda, salt, nutmeg, and cinnamon together to blend.
In a large bowl, using an electric mixer on medium-high speed, beat the sugar and eggs for about 8 minutes, or until pale and thick. Gradually beat in the canola oil. Beat in the bananas, yogurt, and vanilla. Reduce the speed to low, add the flour mixture, and mix just until blended. Using a large flexible spatula, fold the toasted walnuts into the batter.
Spread the batter in the loaf pan. Sprinkle the top with the remaining ½ cup walnuts. Bake for about 1 hour and 15 minutes, or until the top is browned and a wooden toothpick inserted into the center of the loaf comes out clean. If the bread is browned before it tests done, tent the top with aluminum foil. Let cool in the pan on a wire cake rack for 15 minutes.
Invert the banana bread onto the rack and turn right side up. Slice and serve warm, or let cool completely before serving.