Combine the first 5 ingredients (boiling water through light brown sugar) in the bowl of a stand mixer, and let stand 25 minutes.

Combine 1 ¼ cups of the bread flour and all of the whole wheat flour with yeast. Gradually add the flour mixture to the oat mixture. Beat at medium speed until well blended. Turn dough out onto a floured surface. Knead until smooth and elastic (about 8 minutes), adding enough of the remaining all-purpose flour, 1 tablespoon at a time, to prevent dough from sticking to hands if necessary (dough will still feel moist).

Place dough in a large bowl coated with cooking spray, turning to coat top. Cover with plastic wrap, then a clean kitchen towel, and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in size.

Punch the dough down; cover with plastic wrap and let rest 5 minutes. Roll the dough into a 14 x 8-inch rectangle on a floured surface. Roll up the rectangle tightly, starting with a short edge, pressing firmly to eliminate air pockets; pinch the seam to seal. Place the loaf, seam side down, in a 9-inch loaf pan coated with cooking spray. Cover with plastic wrap and let rise 30 minutes or until doubled in size.

Preheat oven to 350º.

Uncover dough and bake at 350º for 45 minutes or until loaf is browned on bottom and sounds hollow when tapped. Remove from pan, and cool on a wire rack.