Preheat the air fryer to 400°F. Use an air fryer liner or cut a piece of parchment paper to fit in the air fryer basket. Spray with cooking spray (use a high smoke point cooking spray like avocado oil), if desired.
Pat the chicken thighs dry on both sides with paper towels and then place them in a large bowl.
Drizzle the thighs with the oil and toss to coat the chicken evenly.
Whisk together the smoked paprika, paprika, salt, garlic powder and black pepper in a small bowl and then sprinkle the seasoning evenly all over the chicken thighs. Rub the seasoning into the chicken until evenly coated.
Place the thighs, skin side down, in a single layer, on the prepared liner or parchment paper (if using) in the air fryer basket. The chicken should not be touching so you may need to cook the chicken in multiple batches.
Air fry the chicken for 9 to 11 minutes, flip the chicken over and continue cooking for another 9 to 11 minutes, until the skin is golden brown and crispy and the chicken has reached a minimum of 160°F internally, use a meat thermometer.
Remove the chicken thighs from the air fryer and allow them to rest for 5 to 10 minutes. (The chicken will continue cooking after removed, to the FDA recommended 165°F internal temperature.)
Serve hot garnished with fresh parsley and/or lemon slices, optional.