Place the buttermilk and egg in a medium bowl and whisk to combine (I add a pinch of salt). 

In a shallow dish or on a large plate, pour the panko and all the spices (garlic powder, onion powder, salt, mustard powder, paprika, and black pepper).  Gently stir together (I just use my fingers).

Put the cornstarch in a large plastic bag.  Pat your chicken tenders dry and put them in with the cornstarch.  Seal the bag and shake around until fully coated.  Shake each piece to remove excess cornstarch.

Working in batches, dip the chicken in the buttermilk mixture, then dredge (and cover) in the panko mixture until fully coated. Place on a plate or baking sheet in a single layer, with a little space between. 

<b>Let rest at room temperature for 30 minutes...this is critical, as it gives the coating time to adhere to the chicken.</b>

Preheat your air fryer at 400ºF for a few minutes. Working in batches as needed, spray both sides of the chicken with a little olive oil.

Arrange the chicken in a single layer in the air fryer basket, leaving a little space between. Cook in the air fryer until cooked through and crispy, flipping halfway through.  It will probably take 9-10 minutes, maybe a bit more.  The fattest part of the chicken tenders should register at least 145 F inside.

Serve with your favorite dipping sauces.  You can refrigerate leftovers in an airtight container for a few days and reheat in the air fryer for 5 minutes, though these are definitely better fresh if possible.