Preheat the waffle iron. Set it to medium or the setting you usually use for golden waffles.
Lightly oil or spray once hot.
Mix dry ingredients. In a large bowl, whisk protein powder, oat or wheat flour, baking powder, salt, and cinnamon until well combined.
Whisk wet ingredients. In another bowl, whisk the egg, egg whites, Greek yogurt, milk, vanilla, and maple syrup or honey until smooth.
Combine. Pour the wet mixture into the dry. Stir gently until just combined. If it’s too thick, add a splash of milk.
The batter should be pourable but not runny.
Finish with fat. Stir in the melted coconut oil or butter. This helps with crispness and prevents sticking.
Cook. Pour batter into the preheated iron, using enough to cover the grates without overflowing (usually 1/2 to 3/4 cup per waffle, depending on your iron). Close and cook until the steam subsides and the waffle is golden and set, about 3–5 minutes.
Hold warm. Place finished waffles on a wire rack in a 200°F (95°C) oven so they stay crisp while you cook the rest.
Serve. Top with fruit, a dollop of yogurt, a smear of nut butter, or a light drizzle of syrup.
Enjoy right away for the best texture.