Combine first 3 ingredients in a 2-cup glass measuring cup; let yeast mixture stand 5 minutes.
Combine 2 cups all-purpose flour, whole wheat flour, oats, and salt.
Beat yeast mixture, 1 cup all-purpose flour, honey, and olive oil at medium speed with a heavy-duty electric stand mixer until well blended. Gradually add whole wheat flour mixture, beating at low speed until a soft dough forms.
Turn out dough onto a well-floured surface, and knead 9 minutes, adding additional all-purpose flour (up to 6 tablespoons) as needed. (Dough will be slightly sticky.) Place dough in a large bowl sprayed with cooking spray, turning to grease top of dough.
Cover bowl of dough with plastic wrap, and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in bulk.
Punch down dough, and divide in half. Roll each portion into a 13- x 8-inch rectangle on a lightly floured surface. Roll up each dough rectangle, starting at 1 short side, jelly-roll fashion; pinch ends to seal. Place loaves, seam sides down, into 2 (8 1/2- x 4 1/2-inch) loaf pans sprayed with cooking spray.
Cover loosely with plastic wrap, and let rise in a warm place (85°), free from drafts, 45 minutes or until almost doubled in bulk. Remove and discard plastic wrap.
Bake at 350° for 30 to 35 minutes or until loaves sound hollow when tapped and are golden. Cool in pans on wire racks 10 minutes. Remove loaves from pans, and cool on wire racks.
Note: If you don't have a heavy-duty electric stand mixer, you may mix dough by hand with a wooden spoon.
Cook's Tip: To measure flour, spoon into a dry measuring cup, and then level the top with a knife. Never scoop the measuring cup into the flour--you'll get too much flour, resulting in a dense, thick bread.