Combine yeast, warm water, and brown sugar and let rest 5 minutes. Using electric beaters, mix in buttermilk, all-purpose flour, 3/4 cup wheat flour, baking soda, salt, and margarine, beating until smooth. Stir in granola and enough of the extra whole wheat flour to form a soft dough.
Knead dough until elastic, about 5 minutes. Separate dough into 2 even portions. Roll each into an 18 x 10 inch rectangle. Roll up and seal. Lay loaves, seam side down in cooking spray coated 9 x 5 inch loaf pans. Let rise, covered in a warm place for 1 hour.
Coat tops of loaves with buttermilk and bake at 375 degrees F for 40 to 45 minutes. Let cool before slicing.