Preheat oven to 425°F. In a large bowl, combine the flours, baking soda, baking powder, and salt. Set aside.In a blender, combine nondairy milk, vinegar, and spinach leaves and blend until completely smooth. Pour all but about 1 Tablespoon of the spinach and milk mix into the flour. Using a spatula or spoon stir into the flour just until combined.Divide the dough into three to make small, 6-inch loaves. Toss some extra flour onto your balls of dough and transfer them to a parchment-lined baking sheet. Flatten them just slightly so that they bakes evenly and slash an "X" into the tops with a knife. Don't go too deep, just a surface slash. If you are sprinkling anything on top, use that remaining Tablespoon of spinach/milk mixture to brush on the loaves before sprinkling the toppings.Bake for 30-35 minutes or until the bottoms are slightly browned and the tops feel crusty.Remove from the oven and transfer to a wire rack to cool. Be sure to throw a clean dish towel over them and let them cool down under it. This will ensure that the loaves stay tender. Enjoy them with vegan butter, preserves, or olive oil.