In a bowl, combine the thawed and squeezed spinach, crumbled feta cheese, fresh parsley, and lemon juice. Mix well until all ingredients are thoroughly combined.
Make a slit in the side of each fillet to create a pocket for the stuffing. Be careful not to cut all the way through.
Spoon the spinach, feta, and parsley mixture into the pockets of each salmon fillet.
Preheat your air fryer to 375°F (190°C) for about 3-5 minutes.
Place the stuffed salmon fillets in the air fryer basket, ensuring they are not touching to allow for even cooking. Air fry the salmon for 12-14 minutes, or until the salmon is cooked through and flakes easily with a fork. The exact cooking time may vary depending on the thickness of the salmon fillets.
Remove the salmon from the air fryer and let it rest for a few minutes before serving. Garnish with lemon slices or additional parsley if desired.