Mix buttermilk and oats in a medium bowl; set aside for 15 minutes while you measure out your other ingredients. Meanwhile, whisk together the whole wheat flour, unbleached all-purpose flour, pecans, cornmeal, baking powder, baking soda, salt, and cinnamon in a large bowl.

Stir the eggs, optional brown sugar, oil and vanilla into the reserved buttermilk-oat mixture. Add the wet ingredients to the dry ingredients; mix with a rubber spatula just until moistened.

Coat a waffle iron with cooking spray and preheat. Spoon in enough batter to cover three-fourths of the surface, about 2/3 cup for an 8-inch round waffle iron. Cook until waffles are crisp and golden brown, 4 to 5 minutes. Repeat with remaining batter. Serve immediately.