Preheat oven to 350˚F. Grease a 9x5 inch loaf pan.
Combine whole wheat flour, all purpose flour, flax seeds, baking powder and soda, pumpkin pie spice, and salt together in a medium bowl.
In a separate large bowl mix bananas, pumpkin, yogurt, sugar, oil, and egg.
Add flour mixture to banana mixture, then fold until just mixed. Do not over mix.
Fold zucchini and nuts in gently.
Add batter to loaf pan. Bake for 60-75 minutes. Insert a toothpick in the center, if it comes out clean, the loaf is done.
Cool on a wire rack for 10 minutes, then remove from pan and cool completely.
Notes
Do not over mix the wet and dry ingredients as it may cause a heavy, dry loaf.
Store leftovers at room temperature in an airtight container for up to 2 days, or refrigerate for up to a week. Store in the freezer for up to 6 months, wrapped in plastic wrap.
It's a good idea to freeze slices between pieces of parchment paper, then in a zippered bag. This makes it easy to grab a piece quickly to pack, or thaw in the microwave.