Prepare your waffle iron. In a large bowl mix together the flour, oats, sugar, baking powder, and salt.
Melt the butter in the microwave. Let cool for a few minutes. In another bowl, beat the egg yolks together. Add the buttermilk to the bowl and whisk, then add the melted butter while whisk. Pour the mixture into the dry ingredients and whisk until combined.
In a separate bowl, combine the egg whites and vanilla extract. Use a handheld mixer or a stand mixer with the whisk attachment. Beat on medium high speed until medium peaks form. Pour half into the batter and fold together until combined, then do the same with the rest.
Spray the inside of the waffle iron with a small amount of baking spray to prevent sticking. Pour in about ¾ cup to 1 cup of batter and spread gently. Close and cook about 2 minutes or less on each side. You may need to decrease or increase the time dependent on your waffle iron. When done, remove with tongs and set aside, and repeat the process until out of batter.
To serve, toast your desired amount of pecans in the oven or on the stovetop - I used about 1/4 cup per waffle serving. Spread each waffle with a thin layer of quality butter, then top with a dollop of Greek yogurt. Sprinkle with the pecans, whole or chopped, then drizzle with your favorite maple syrup.