Preheat the waffle iron on medium-high, following its instructions, and spray it with cooking spray.
In a bowl, whisk the oat flour, protein powder and baking powder.
In a second bowl, whisk the eggs, Greek yogurt, milk and vanilla, then fold into the dry ingredients until just combined. Rest 3 minutes.
Spoon about half the batter into the iron, spread it towards the edges, close and cook for 4 to 5 minutes, until golden and the steam has mostly stopped. Repeat with the rest, spraying again.
Keep the first waffle warm and crisp on a rack in a 90°C (200°F) oven while the second cooks.
Serve topped with sliced strawberries and maple syrup.