Whisk the flour and spices in a large bowl. In a small deep bowl, whisk the egg, butter, and milk.
Place the onion in a large clean bowl, cut-side up and separated.
Sprinkle the flour mixture over the onion getting in between the layers. I used a fork to sprinkle the flour mixture, and used my fingers to separate each individual layer and sprinkle the flour between every petal.
Dump the remaining flour over the whole onion. Let it sit for a few minutes.
Turn the onion over and gently pat off the excess flour back into the bowl. Reserve the remaining flour. You want to make sure the flour coats the petals without leaving large clumps of flour in between the petals.
Transfer the onion into a large bowl and pour the egg mixture over the onion and coat evenly. Pouring over the onion helps it to get in between the petals and coat the flour.
Open each petal to make sure the egg mixture soaks every bit of flour between the petals. Let the onion sit in this mixture for a few minutes. Remove the onion from the bowl and let the excess drip off.
Add the packet of seasoned coating mix to the leftover flour mixture. Place the wet onion into an empty bowl or onto the aluminum foil and sprinkle the reserved flour and coating mixture over it. Do not sprinkle in between those petals as it will be difficult to spray with cooking oil afterwards. However, sprinkle the flour and breading mixture over every part of the onion that is exposed to the air. I will even brush more egg mixture over drier parts of the onion to get as much mixture there as possible.
Place the onion into the refrigerator to set while you preheat the air fryer.