Preheat the oven to 350°F. Spray an 8½ x 4½- inch loaf pan with cooking spray.
Lightly spoon the flour into dry measuring cups and level with a knife. In a medium bowl, whisk together the flour, baking soda and salt.
In a large bowl, use an electric mixer to beat the sugar and butter together on medium- speed until well blended (about 1 minute). Add the banana, eggs and yogurt; beat until blended. Add the flour mixture; beat at low speed just until moist.
Place the chocolate chips in a medium microwave- safe bowl, and microwave on HIGH for 1 minute or until almost melted, stirring until smooth. Cool slightly. Add 1 cup of the batter to the chocolate, stirring until well combined. Spoon the chocolate batter alternately with the plain batter into the prepared pan. Swirl the batters together with a knife.
Bake for 1 hour and 15 minutes, or until a wooden pick inserted in the center comes out clean. Cool 10 minutes in pan on a wire rack; remove from pan. Cool completely on a wire rack.