Preheat oven to 350°F. Grease and flour a 9-by-5-inch loaf pan. Whisk flour, baking soda, baking powder and salt in a medium bowl.
In a large bowl, using an electric mixer on medium speed, beat together bananas, sugar, egg, oil, orange zest and 1/2 cup water until thoroughly combined, about 3 minutes. Reduce mixer speed to low and add flour mixture in 2 batches, beating after each addition until just combined. Scrape down sides of bowl.
Stir in walnuts, chocolate chips and oats. Pour batter into loaf pan and bake until bread is golden brown and a skewer inserted into center comes out clean, about 1 hour. Cool loaf in pan on a wire rack for 10 minutes, then remove from pan and let cool completely.