In a large bowl, whisk together flour, oats, sugar, baking powder, baking soda and salt.
In a smaller bowl, whisk together buttermilk, eggs, butter and vanilla.
Add buttermilk mixture to dry ingredients, stirring until combined. Let batter rest while waffle iron heats.
Spray waffle iron with cooking spray.
Ladle batter* into iron, close lid and cook until waffle is golden and releases from the iron easily. Repeat with remaining batter.
Waffles should be served immediately, or can be kept warm in a low (200°F) oven until all have been cooked.
Serve with butter and maple syrup, or yogurt and fresh fruit.
*Note: waffle irons vary in size, use the recommended amount of batter for your iron.