In a large mixing bowl, sprinkle the yeast over the water and set aside for 5 minutes, or until frothy. Whisk together the buttermilk, oil, sugar, and flour until smooth. Refrigerate the bowl overnight, covered in plastic wrap.
Preheat the waffle maker. In a separate bowl, whisk together the oats, egg whites, baking soda, and salt until smooth. Spray the hot waffle iron lightly with cooking spray. Spread about 1/3 cup batter over the borders of each portion using the back of a spoon. Cook for 5 to 7 minutes, or until the waffles are crisp and golden brown. Rep with the rest of the batter. With maple syrup on top.