In a large bowl, combine oat flour, baking powder, cocoa powder and salt. Whisk together to combine then stir in hazelnut pieces.
In separate medium bowl, whisk the eggs. Add remaining ingredients and whisk until completely combined. Pour into dry mixture. Stir together until just combined, small lumps in the batter are fine. Let the batter sit and thicken for 10 minutes while you heat up waffle iron.
Pour about ½-cup batter into center of heated greased waffle iron. Cook each waffle according to waffle iron directions, usually 3-5 minutes.
To keep waffles crisp while cooking large batch place them on wire rack in oven at 200 F.