Preheat the oven to 425 degrees F.
In a large bowl, whisk together the flours, baking soda, oats and salt. Pour in most of the buttermilk and mix well, adding more buttermilk, if needed, to form a soft dough. Turn out onto a floured surface and lightly knead into a shapeable dough. Avoid overworking the dough. Shape the dough into a round disk shaped loaf and cut a deep "X" in the top with a sharp knife. Put the dough on a parchment lined baking sheet and bake for 7 minutes at 425 degrees F. Lower the oven temperature to 375 degrees F and bake another 20 to 25 minutes. Remove the bread from the oven to a cutting board. Cool slightly before cutting and enjoy warm!