Marinate: Preheat air fryer to 375 degrees F (190 C). Clean mushrooms then toss together with buttermilk in a large bowl. Let marinate for 15 minutes.
Breading: In a large bowl combine flour and spices. Spoon mushrooms out of the buttermilk (save the buttermilk). Dip each mushroom in the flour mixture, shake off excess flour, dip once more in the buttermilk, then once more in the flour (in short: wet > dry > wet > dry).
Cook: Grease the bottom of your air fry pan well, then place mushrooms in a single layer, leaving space between mushrooms. Cook for 5 minutes, then roughly brush all sides with a little oil to promote browning. Continue cooking 5 to 10 more minutes, until golden brown and crispy.
Make vegan buttermilk by combining 1 1/2 Tbsp lemon juice + 1 1/2 cups plain soy milk.
*Alternatively, spritz with cooking spray for even coverage and less overall oil.