Preheat oven to 350°F. Oil an 8-1/2 x 4-1/2 inch loaf pan.
In a large bowl, sift together unbleached white flour, whole wheat flour, flaxseed meal, baking powder, cinnamon and cardamom (if using). Set aside.
In a separate bowl, mash bananas and stir in lemon zest (if using). Set aside.
Mix oil, sugar and salt until incorporated. Add eggs and vanilla and mix until well combined.
Add flour mixture to sugar mixture, alternating with bananas. Scrape down the sides of the mixing bowl often.
Pour batter into the prepared laof pan and tap lightly on the counter to release any air bubbles.
Bake at 350°F until the sides of the loaf begin to pull away from the pan and a toothpick inserted into the center comes out clean, about 50 - 60 minutes.