In a bowl, mix ricotta, spinach, harissa, black pepper, and salt until fully combined.
Pat salmon fillets completely dry with paper towels to remove surface moisture.
Using a sharp knife, slice each fillet horizontally halfway through to create a pocket.
Divide the ricotta mixture between fillets, stuffing it into the pockets and pressing gently to seal.
Preheat the air fryer to 390°F and spray the basket with nonstick cooking spray.
Place stuffed salmon in the basket, stuffed side up, leaving space between fillets.
Cook for 16–18 minutes until the salmon flakes easily with a fork and the internal temperature reaches 145°F.
Let rest for 2 minutes before serving.