Heat a waffle iron. Whisk together the flour, cornmeal, sugar, baking powder, poppyseed, baking soda, and salt in a large bowl.
Put the lemon zest and juice into a medium bowl. Whisk in the whole eggs, yogurt, milk, butter, and oil. Pour this mixture into the dry ingredients and stir until just combined; the batter should be slightly lumpy.
Whip the egg whites with an electric mixer on medium-high speed until stiff peaks form when the beaters are lifted, 1 to 2 minutes. Gently fold the whites into the batter.
Spoon about ⅔ cup of batter onto the hot waffle iron, gently spreading it to cover the entire surface. Close the lid and cook until the waffle is golden brown, 5 to 7 minutes.
Tip: Keep waffles warm in a single layer in a 200ºF oven. To prevent sogginess, avoid stacking them on plates. Freeze any leftover waffles in a ziplock bag for up to six months. Reheat in a toaster or 325ºF oven.