Marinate the Chicken: In a large bowl, whisk together the buttermilk, garlic powder, onion powder, smoked paprika, black pepper, and salt. Add the chicken thighs, ensuring they're fully submerged. Cover and marinate in the refrigerator for at least 1 hour, or up to overnight for maximum flavor.
Prepare the Breading: In a shallow dish, combine the flour, panko breadcrumbs, and a pinch of salt and pepper. Mix well to incorporate.
Coat the Chicken: Remove the marinated chicken thighs from the buttermilk, allowing excess to drip off. Dredge each thigh in the flour mixture, pressing it in to adhere, and then shaking off any excess.
Preheat the Air Fryer: Preheat your air fryer to 380°F (193°C) for about 5 minutes.
Air Fry the Chicken: Lightly spray the air fryer basket with cooking spray. Place the coated chicken thighs in a single layer, making sure not to overcrowd them (you may need to do this in batches). Lightly spray the tops of the chicken with cooking spray. Air fry for 20-25 minutes, flipping halfway through, until golden brown and cooked through (internal temperature of 165°F or 75°C).
Prepare the Gravy: While the chicken is cooking, heat the creamy mushroom gravy in a small saucepan over low to medium heat. Stir occasionally until warmed through.
Serve: Once the chicken is done, remove it from the air fryer and let it rest for a few minutes. To serve, place the chicken on a plate, generously drizzle with warmed creamy mushroom gravy, and garnish with chopped parsley.