Prepare your breading station with four shallow dishes: Pour ½ cup milk into the first dish, combine ½ cup all-purpose flour with ½ teaspoon garlic and onion seasoning in the second, fill the third with ½ cup ranch dressing, and mix ¾ cup panko bread crumbs with 2 tablespoons dry ranch dressing mix in the fourth.

Take the cleaned portobello mushroom caps and dip each into the milk, ensuring they're fully coated. Dredge them in the flour mixture, then coat in ranch dressing, and finally roll in the panko mixture until fully covered.

Place the coated mushrooms in a single layer in the air fryer, spray tops with nonstick cooking spray, set to 400°F and cook for about 7 minutes, or until crispy and lightly browned.

Once done, remove from the air fryer and serve immediately while hot and crunchy, paired with ranch dressing, garlic aioli, or marinara sauce.