In a medium bowl combine flour with cornstarch, garlic powder, smoked paprika, chilli powder, oregano and salt. Add egg and gradually whisk in milk until smooth.
Cut onion into ¼ inch (6mm) slices. Carefully separate the rings of onion.
Coat onion rings in flour mixture and let the excess drip off.
Coat the rings in breadcrumbs and repeat until all rings are done.
Heat oil into a skillet or pan.
Fry the rings, in batches, until they are golden brown, for about 2-3 minutes.
Transfer to a plate lined with paper towel to remove excess oil.
Serve with your favorite dipping sauce.